These are TLR22 pistons.. You can buy the standard 22 pistons, which are 4 hole, however, to make them '2 hole', you must CA glue two holes, diagonally across from each other.
The TLR 22 pistons are p/n "TLR5090" and you can buy them from A Main!
http://www.amainhobbies.com/product_...ngs-Set-TLR-22