You'll need an MR2 specific subframe for the seat.
AFAIK, the only ones on the market (which fit) are Bride, and you normally have to ship them from Japan. That's where I had to get mine from!
Oh, and AFAIK, the Bride subframes only fit Bride seats?
its a huge mismatch, several people make subframes for mr2s but not everybodies fit every seat, big differences come with fixed and reclining bucket seat aswell (think the fia have specific dimesnion needed for approval), for instance i've got a bride subframe for a fixed seat with a corbeau forza sport on it, however a corbeau clubman and carrera seat dont fit it it is easy to adapt the original subframes to fit new seats though, just need a grinder, hacksaw and a drill