I would suggest googling Toyota MR2 performance engine parts, should be something there.
one of my friends used CP pistons with eagle rods and bored to 86.5mm +.020/+0.5mm . if thats not what your looking for i would go to a local shop.
There should be vendors on two big MR2 boards, www.mr2oc.com and www.mr2.com. Off the top of my head I can think of ATS Racing (atsracing.net) for strokers, and they can probably hook you up with pistons too.
JE Pistons http://www.nolimitmotorsport.com/prod/JE162109 Wiseco Pistons http://www.nolimitmotorsport.com/prod/K615M865 http://www.nolimitmotorsport.com/prod/K615M87
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