First things first. Without the proper tools, the new parts you install might not fix the problem, and it sounds like you had something rubbing, possibly due to the bearing. You can buy the bearings and brushes at a good parts store, they need either the old parts or the number off your generator. It's important to check the coils, check the rotor with a growler, and to turn the commutator on a lathe followed by recutting the grooves.
You can buy rebuilds, my luck with older generators has been good. Better if you can find an old electrical mechanic to rebuild it for you. I rebuilt them in a shop in the 70's, but don't do them myself because I don't have the tools.
