If a man does not have a redeemer

From parashat Behar, the following pasuk and Rashi:

26. And if a man does not have a redeemer, but he gains enough means to afford its redemption,		כו. וְאִישׁ כִּי לֹא יִהְיֶה לּוֹ גֹּאֵל וְהִשִּׂיגָה יָדוֹ וּמָצָא כְּדֵי גְאֻלָּתוֹ:
And if a man does not have a redeemer: But is there a man in Israel who has no [relative] to redeem [his sale]? However, [Scripture means] a redeemer who is [financially] able to redeem his sale. — [Kid. 21a]		ואיש כי לא יהיה לו גאל: וכי יש לך אדם בישראל שאין לו גואלים, אלא גואל שיוכל לגאול ממכרו:

The context is when someone sells a sdei achuzah, inherited land. And the gemara this is based on, Kiddushin 21a, reads:

דתניא  (ויקרא כה, כה) וגאל את ממכר אחיו רשות אתה אומר רשות או אינו אלא חובה ת"ל  (ויקרא כה, כו)

ואיש כי לא יהיה לו גואל וכי יש אדם בישראל שאין לו גואלים אלא זה שיש לו ואינו רוצה ליקח שהרשות בידו דברי רבי יהושע ר"א אומר וגאל את ממכר אחיו חובה אתה אומר חובה או אינו אלא רשות ת"ל בכל גאולה תתנו הכתוב קבעו חובה

The Taz, in Divrei David, discusses a question raised and answered by other supercommentators of Rashi: Namely, in parshat Naso, where someone swore falsely and caused another party to lose money, he needs to make restitution, plus 1/5th. Then, the pasuk, together with Rashi, states:

8. But if the man has no kinsman to whom to make restitution, the debt which is restored to the Lord, [is to be given] to the kohen. [This is] besides the atonement ram through which expiation is made for him.		ח. וְאִם אֵין לָאִישׁ גֹּאֵל לְהָשִׁיב הָאָשָׁם אֵלָיו הָאָשָׁם הַמּוּשָׁב לַי־הֹוָ־ה לַכֹּהֵן מִלְּבַד אֵיל הַכִּפֻּרִים אֲשֶׁר יְכַפֶּר בּוֹ עָלָיו:
But if the man has no kinsman: For the claimant who made him swear has died, and has left no heirs.		ואם אין לאיש גואל: שמת התובע שהשביעו, ואין לו יורשים:
to whom to make restitution: when this one decided to confess his sin. Our Sages say: Is there any man in Israel who has no kinsman-either a son, a daughter, a brother, or some other relative from his father’s family-all the way back to our father Jacob? Rather, this is [referring to] a proselyte who died, leaving no heirs. — [Sifrei Naso 1:23, B.K. 109a, Sanh. 68b] [since a proselyte is judged as a newborn, without relationship to those born prior to his conversion.]		להשיב האשם אליו: כשנמלך זה להתודות על עונו. ואמרו רבותינו וכי יש לך אדם בישראל שאין לו גואלים או בן או אח או שאר בשר הקרוב ממשפחת אביו למעלה עד יעקב, אלא זה הגר שמת ואין לו יורשים:

The Taz notes the divergence, and then gives the answer of Maharan as well as Gur Aryeh that the topic in parashat Behar is an inherited field, and just whom will this convert inherit a field from? Taz objects that he can construct such a case, in which he got one from an Israelite in a walled city and the original owner did not redeem it within a year. Then, it belongs perpetually to that convert. He then suggests that Rashi did not put this forth because it is much better to have it deal with an absolute Israelite, in its simplest meaning, who does not have a redeemer.

I read a little bit more (see Mizrachi and Gur Aryeh) and I am not convinced that the question even starts. It seems to me to be built on a faulty premise.

Is Rashi the author of these midrashic statements? Surely not! Rather, he is applying existing midrashim, in the gemara, in the Sifrei, etc., to pesukim. He will not invent a midrash halacha out of whole cloth. Now, the Rashi in Naso is based on the aforementioned sources, namely the Sifrei, and the gemara in Bava Kamma and Sanhedrin. There, Rabbi Akiva renders this interpretation as referring to the convert, by restoring gezel hager. But I do not see that Rabbi Akiva applies to redeeming sold inherited land. Maybe Rabbi Akiva would extend it, or maybe not, but that is not the topic there, and so he does not say it. Similarly, over here, Rabbi Yehoshua says that it applies to whether there are any voluntary redeemers of the land. It is true that it would not make sense to apply this to receiving restored stolen property. While people might be reluctant to outlay money to purchase something, who would object to receiving free money?! Still, perhaps Rabbi Yehoshua would apply it to the case of receiving money as well. But we don't see him say this! Of course, Rabbi Yehoshua's disputant would need to explain the pasuk, and could then adopt the famous "ger" explanation. Yet, I don't see anyone saying this in Kiddushin explicitly. (I could be wrong. Does anyone spot an  instance such a derasha occurs?)

If so, what is Rashi to do? While he does occasionally venture into his own suggested peshat, a good portion (I would estimate >80%) of his commentary consists of selections from midrash aggadah and midrash halacha. I do not believe it reasonable to expect Rashi to manufacture a midrash halacha, even if that involves applying a midrash halacha from one place to another. Rather, he reports what he does because that is what is available to him in the Rabbinic literature.

Therefore, it seems misguided here to wonder just why Rashi did not apply one midrash halacha to a foreign location.  One could ask why Chazal don't apply it, but the answer may be that they do, though non-explicitly. This often occurs: supercommentators of Rashi take up midrashic questions, and end up inventing reasons for and facets of midrash.

Granting the legitimacy of the question for the sake of discussion, my impression is that Rashi in Behar is indeed works much more nicely on the level of peshat. I suppose one can read "no goel/karov" as meaning "convert", but to say it is a regular Israelite makes more sense. This before one arrives at any difficulties in arranging a convert with sdei achuza. Even though it is possible to construct such a case, it already seems farfetched. Meanwhile, not convincing someone to be the goel is a regular occurrence.

Of course, this does not work in Naso, for the reason already given. Who will turn down receiving free money? And perhaps a global explanation makes for better peshat.

Another possibility is that in the instance of recompense, the man has no identifiable close relatives. People move about from town to town, and perhaps they do not know his lineage. And of course he is related, distantly, to any other Israelite, but there is no real sense that paying back any random extremely distantly relates Israelite off the street is really paying his family back. This on a peshat level, though not necessarily (or probably) reaching the level of halacha.