That thing between the transmision and the floor

[old Chevy guy]

My son and I are doing a frame off ,ground up restoration on his 90 s10 2wheel drive pickup. We have the frame sandblasted , painted and Lowered .Tommorrow we will pick up the resurfaced flywheel so we can put the motor back together with the tranny with the new clutch and install it back on the frame.Then we will be ready to put the cab back on.Which brings me to my question,where can we get that gasket thing that goes between the floor and the top of the transmission? Does someone make that as a replacement part? Some mice chewed up the old one.