SPI, sports parts inc., is just an import distributor so you often won't find them advertised at the retail level as SPI. Usually marketed as "original replacement" or "kimpex", or "piston and ring kits" or ? Last batch I ordered some came in "parts unlimited" boxes, some in "SPI" boxes. They are made by namura (sp?) in taiwan BTW.
Where I sled: Around town and Christopher / Emma Lakes
I've never seen them in Royal Distributing catalogue, but I have seen them in the Recreation Supply catalogue. Rec Supply lists SPI as a separate brand and I thought they are a forged piston, similar to Wiseco, and come with coated skirts and domes.