Any and all RWS parts can be had at Umarex USA. Just Google it. They have breech seal shims and all other parts for RWS guns. Although if i were looking for a spring or piston seal, I would go to James Maccari. He just did custom guides fitted to a spring for a RWS 460. MINT!!! He also carries custom setups for 48, 52, and 54's. I just finished 4 48's, 5 52's, 5 54's and 2 460's of both .177 and .22 calibers. All got JM piston seals and breech seals with Umarex used for other parts. These are wonderful air rifles and a real pleasure to work on. Today started mounting scopes on 4 more. Again, it's more fun than work. Lee
There are some threads in this forum about the shims. Rob Hawkins was handing them out for free at the time (great job Rob). Rob's were a correctly sized nylon washer. If he is out, perhaps you could get one at a hardware store with the right specs. I could measure one, but it wouldn't be too precise, so I'm hoping for others to chime in once they understand the post is about shims, not seals....