Further to the Italeri offerings the PSC have a nice duel option kit with the 57mm and 76mm AT guns being available as alternative variants. The number of guns in the pack are nice too, as in four (see below):
The Zis 3 76mm AT Gun and servants (see below):
The Zis 2 57mm AT Gun and servants (see below):
I must confess I was slightly taken aback with the length of the 57mm AT (Zis 2) Gun's barrel. It must have had a heck of a mussel velocity but just did not pack the punch to trouble a Panther or Tiger, so it was replaced by the Zis 3 76mm gun.
Correction: Please read comments for the "real" reason ;)