I have a Daisy 1270 chrome plated with black plastic grips and forend.These and the 1200 etc are quite scarce in the UK in large part because until 1997 Co2 was available only on license,so off ticket springers and a few PCP pistols ruled!Sorry I can't help with O ring sizes,but I'm sure you'd get the info you need from one of the American forums.
Actually,you could try and PM ''Lawrie armatruda'' on here,he repairs Co2 and pumpers,so will very likely know!