I have a 20 year old Beeman R10 that is in great condition.

I would like to replace the main-spring with a gas-piston...similar to the RX-1 and Cro-Magnum but I can't seem to find anyone who does it.

Any of you have a suggestion for me?

PS: I had an old R1 with a gas piston but I sold it to pay for a Benjamin Marauder...BIG MISTAKE!

Leopard, might check with these folks:
http://vortekproducts.com/ourstore/

The old Beemans are things of beauty. I did briefly have a .25 Marauder and was very impressed with how quiet, accurate and powerful it was. I had just had back surgery, however, and operating the Hill pump was not in my best interest.

Im going to check out your link, thanks!

Me too...I have a Marauder and its a pain in the ass to have to either pump it or fill a scuba tank which isn't good for more than a few full charge fills.

I might sell the R10 and Marauder and buy a used RX2

If you have access to a firehouse compressor, get a used SCBA 88cu.ft firemans bottle( eBay has tons of them for sale). They fill to 4500psi, giving literally dozens of fills for a Marauder.