Quote Originally Posted by nige346 View Post
The colour's not important, Seals are often coloured for the industry they are used in (ie green/blue are often used in the food trade) you will need either polyurethane or Silicon for CO2, If the seal is to be moved on a regular basis (ie Cylinder to pistol seal) you will need Polyurethane as silicon will be too soft. Protek may have some but failing that Kent Bearings and Seals in Rochester or Seal Force, You'll get a pack of 10 for about the same price as one from Walther, Brand/colour isn't important at all, an O ring is an O ring as long as it's the correct material & size.
What Nige said is correct about aftermarket suppliers. Had good experience with Seal Force - you can find them *b*y