A good deal on aftermarket bull barrels and stocks? Well, for barrels you can visit
http://www.gmriflebarrel.com/, or more specifically
http://www.gmriflebarrel.com/catalog...iameterBarrels
Good stocks aren't cheap, but Houge makes pretty good ones... but don't count on using them for a sling or on them being SUPER accurate.
http://www.getgrip.com/main/overview/overmolded.html (see the 10/22 section). Another (NOT cheap) alternative is
http://www.mcmfamily.com/mfsinc_n/ruger.html
To be honest, the best upgrade you can get is a better trigger. If the trigger is a POS, then you can't squeeze the trigger right and your groups will be crap. However this is for more competitive shooting. For casual plinking, what you've got is fine. If you want more information, send me a PM, and I will help you out best I can!
Want more? Check out
http://rimfirecentral.com/forums/ Those dudes are SERIOUS about their 10/22's! :P