Ex850R Alfa Romeo ones fit easily iirc but they certainly want too much money now the wreckers know people want them....
If you can do a bit of steel cutting , welding and drilling you can make adapted bases for any seat, mck it with cardboard?
A BIT OF ANGLE STEEL FROM HARDWARE (oops caps) but look online , look on here , its been done a lot.
Im no trainer , i dont know your skills , give it a bash , be sure its welded well if you weld , put extra screwws and rivetts in if you rivet , overkill is good!