TRD makes oem and oversized pistons for the blacktop engine. They also make a lot more parts for it also to include the ITB adapter (which you can get from celicaRA45 from this board).
Anyway...here is the site.
http://trdparts.jp/english/parts_engine-3s-ge.html
They are a little expensive, about $1100.00 bucks american. unfortunately not a lot of people made pistons for this engine. Other makes will not work with the blacktop due to they have to be specially made because of the valve angles.