Try a NAPA store,I have had good luck there,As long as you do not get a young kid that knows nothing but CPU.Look for a older guy that can read the parts books.IF there is a tag on it take it too,Or any numbers that are on it you will be OK.I think that the Roch 2 Barrel has the same size cup on it and I know you can get those.If you are carefull you can pull it off and put on your shaft, if 2 B is not the same.
Make sure CK ball is not stuck. They have a habit of sticking.It the ball under pump.
Good luck Dale