I think Toyota sells pistons in larger sizes for bored engines... .040" may be the largest they carry though. If anyone feels like it you could research the part numbers on this page:
http://www.cygnusx1.net/Supra/Librar...rts/13101.aspx
Regardless, I'd still go aftermarket. If you're going to have it all apart the wallet is the only reason to reconsider forged internals. At this point I'd go with some GOOD pistons (wiseco or probe, for example) and forged rods.
If money's tight, NPR makes a stock replacement which is available with a Teflon coating. They're affordable and will perform well enough for slightly modded cars. They are still cast though and you have them balanced and matched, but they're pretty good.