This Barrel/Paint Matching Chart
will give you a rough idea of what fits your barrel. There are others not on the list which will likely fit well... Kick'n, WGP, etc.
Shockers have a history for being VERY gentle on paint. There was even a paint which was advertised as too brittle for any other marker but the shocker (SmartPaint). It wasn't true but it is true that they don't commonly break/chop.
I take it that you don't play at a FPO field. If you can choose what you shoot than try RPS Marballizers. Its extremely consistent but you pay a premium for that quality. I was forced to shoot (what appeared to be old and ill cared for) WGP Rec-ball. It broke on the floor if rolled off the table top.
I don't know how fields get away with selling stuff like that but.... although the paint broke while still in the loaders and pods... if it got to the breach on my Shocker, it got to the target.
I really wouldn't stress too much about your shocker having trouble with paint.
Just keep it in good order, have fresh batteries in it and your loader and it will do the job.