Are you aware of any minhagim regarding collecting pieces from broken Tenaim plates to bring about other shidduchim or other good things?
As far as I know there is no source for such a minhag.
Segulas Rabosaynu pg. 231 in the name of R’ C. Kanievsky shlit”a, also see footnote there from R’ B. Z. Mutzafi. As a side point, there are those who say that one of the reasons that people cover the glass cup that the chosson breaks under the chuppah, is in order that no pieces of glass get lost, because they might get used for kishuf.