just go to **** depot and find the right size you need. they're like 20 cents each, are you really THAT stingy?
edit, thats if they are gun orings, as for tank orings if you're running co2 i know you need the tank orings, just get a pack of 10 BE orings from walmart, they work good enough. im using a bunch of orings from the hardware store in my cocker and they work fine.