I poked around in the store at Printrbot.com, and found bearing blocks, but they ask for a password before viewing. No idea what that's about.
A lot of models use stock linear bearings, LMxxUU or LMxxLUU (the xx is the diameter in mm), but some require special press-in bearings. It's been discussed here before, so try searching for your model and bearings.
I still have the original LM12UUs in my KCSP, bought a spare set when I first got it since the originals were sticky but cleaning and relubing fixed it and the replacements are in the spare parts box. Keep your rods clean and regularly lubed, and since the Z bearings don't get a lot of use they should last a very long time. OTOH, the X and Y bearings don't last as long, and my X and Y bearings have been replaced, the X axis twice, in the 4 years I've had it.
Modified KickStarter Classic Plus 7/2012
KS Thingybot Delta Pro 10/31/16