John,
It depends entirely on the condition of the races ... the ball bearings can be purchased very inexpensively from any industrial bearing supply store. If the races are pitted/worn badly enough that you can feel ridges, or pits with a 'fingernail test' then just replace the whole CV-joint, Otherwise, you can repack them with a high-temperature moly grease and use them again with undamaged boots, or new boots if needed.
There are a couple of really great web pages about Lobro CV-joints with procedures and pictures below:
http://www.type2.com/bartnik/cvjoints.htm
http://volksweb.relitech.com/cvjoints.htm
------------------
Warren Hall
1973 911S Targa