There is no "apolytikion" version of "Τον τάφον Σου, Σωτήρ". It is a "kathisma" chanted in soft chromatic scale, as do all prosomoia that follow its melody.
As discussed in earlier posts in this thread, this does not necessarily seem to always be the case, perhaps depending upon schools of chanting and local traditions. This is mentioned, for instance, by Prof. Makris, when he says that,
Well, this phenomenon [i.e. that of an automelon having one scale and melody when it is a kathisma hymn, and another when it is the basis for an apolytikion] is found not only in connection with "Kateplagi Iosif" and nenano, but also with "Ton taphon sou Sotir". (emphasis added)
If an apolytikion is composed according to this kathisma, is will not be sung with the phthora of the second mode (like the original kathisma), but like the other apolytikia of the echos, in "normal" first mode from Pa.
Even the apolytikia that follow the kathisma "O ypsotheis en to Stavro", which is in fourth mode, are not chanted exactly like this, but like the other apolytikia of the mode (same scale, different melody).
It seems that the tradition required that all apolytikia of each mode should have the same "sound". Georgios Rigas wrote against this traditional practice. He believed that the original melodies of the kathismata should be used instead.
This is what I'm basing my comments on, and also and the reason for my request/search for music for the "apolytikion" (i.e. diatonic) version of Τον τάφον Σου, Σωτήρ.
I am aware that yes, in some places, the soft chromatic "kathisma" version of Τον τάφον Σου, Σωτήρ is used as the basis, even when a hymn is actually chanted as an apolytikion. This is how Papa Ephraim writes it in his
Apolytikia and Kontakia for the Entire Year book. This is also how I remember hearing it at the metochion of Simonopetra in Thessaloniki, and also at Simonopetra itself, when I was there last November. However, as mentioned by Prof. Makris above, by my own teacher, Dr. Karanos, and also by Dr. Giannoukakis, I believe, in previous posts (unless I misunderstood him), there is a diatonic version of Τον τάφον Σου, Σωτήρ, which serves as the model melody for apolytikia composed according to this paradigm (e.g. the apolytikion of St. Mary Magdalene, whom we celebrated yesterday.)
-Gabriel