Why not just fab an adaptor between an easily availible poly mount and your transmission? That is what I plan to do with mine when I build the new crossmember this summer.
In fact, it would seem like you could take the broken rubber mount apart and reuse the plate and bolts for a part of the adaptor, then just fit that to the new mount.
Drilling new holes in the crossmember to fit almost any mount is no problem, at worst might have to weld a flat plate over the existing holes and redrill that.
Just my thoughts...