if you're just doing the standard orings on the bolt and hammer, all you'll need is the ones you'll find at any sporting goods store or whatnot for paintball guns. most of the time the orings are that one standard size..
yeah, my friends used to have eradicators... rediculously simple markers, but also rediculously fun to play with... there's a little more strategy involved when you're playing with something strictly semi auto.
Heh, yeah. The gun seems like it would be a lot of fun - loud, simple, and hell, whichever version my friend gave him, it came with a fully functional red dot scope. My cousin came home with the elbow broken, the battery missing from the scope, and paint ALL OVER the inside of the hopper AND marker. There was paint on the hammer, for God's sake. Nonetheless, it wasn't that hard to clean, and he had put too much paint in the hopper. He said every time he'd shoot, the lid would fly open.
Wonder how he broke the elbow, though...now the grav-feeder just feeds directly to the gun.