הלכה על מנחות 85:4

Indeed in Midrash Rabbah Bamidbar (Parshat Shelach, chapter 17) and Tanhuma (ibid) we read: "And now we have only the white (strings of the Tzitzith), for the Techelet was hidden." Aside from the fact that this passage requires elucidation, based on our earlier statement, for how is it that we find no reference or indication in the Talmud to the effect that the Techelet was hidden, this passage is indeed perplexing, for we know that the Midrash was edited during the early period of the Amoraim, by Rav Tanhuma and Rav Ashya Rabbah, and we find explicitly indicated in the Talmud that the Techelet was to be found even among the later Amoraim as indicated in the previously mentioned passage in Menachot (42b) "Abaye asked Rav Shmuel the son of Rav Yehudah," see there. Also see (ibid 43a) "Mar of Meshke once obtained in the time of Rav Ahai some Techelet," see there. We know the opinion of some that Rav Ahai was of the Rabanan Savorai (the Rabbinic period following the Amoraim, sixth-eighth century CE) and in any case, we may derive from the Tosafot in tractate Ketubot (2b) that he was of the last period of Amoraim, for he lived during the time of Rav Ashi. If so, how did the early Amoraim say that the Techelet was hidden?