הלכה על פאה 7:5

Indeed the removal of this claim is quite clear, being that we found no place in the Talmud that tells us that at any particular time that "Techelet" was hidden. For we do find at the end of tractate Sotah that they consider and mention those objects that were lessened and eventually ceased to be found after the destruction. And even those things that were to be found but whose abundance was greatly lessened were also mentioned, as it is written (Sotah 48b) "From the day that the First Temple was destroyed song and fine silk were abolished " and see Tosafot (Shabbat 20b Anan) but in any case they are (ie. song and fine silk) to be found, they are somewhat commonplace, see there. Also white glass is mentioned there, and see Tosafot (Baba Metzia 29b B'Zchuchit) but nonetheless they are still somewhat commonplace, see there. As so too, the flowing honeydew as is mentioned in tractate Sotah (ibid) that it ceased. And yet in the Jerusalem Talmud (Peah, chapter 7 law 3) it seems that it was also found after the destruction. And if indeed the "Techelet" was hidden and ceased to be, the Talmud would certainly have mentioned it in this connection. And in any case, would not have failed to let us know about this anywhere in the Talmud. And from this it seems clear that it was not hidden, nor did it cease to exist and to this we need not even give a thought; for at no time was its existence changed, and it was always difficult to obtain, as tractate Menachot points out (43a) "And it was sold dearly," see there. Also an expert and artisan, one proficient in the making of the dye, was also needed, as is implied there (Menachot ibid). And now too after the destruction of the Temple, its acquisition is no more expensive than during the time of the Temple. And its location is ascertainable with Blessed Divine Help, through an expertly skilled artisan.

From the laws of the commandment is that which they, may their memory be blessed, said (Mishnah Peah 6:5), "Which is fallen grapes? That is one or two [grapes]" that separate from the cluster at the time of the grape harvest." But three [grapes]" that fell at one time "are not fallen grapes." If he was harvesting and he threw them to the ground, when he removes the clusters, even half of a cluster that is found [all separated] there is fallen grapes; and so [too,] a whole cluster that separated there, behold it is fallen grapes. And [regarding] the one who places his basket under the vine at the time of the grape harvest - behold, this one robs the poor (Mishnah Peah 7:5). [These] and the rest of its details are in Tractate Peah (see Tur, Yoreh Deah 332).