The commutator stick that I've seen was a type of pumice designed for motors, I bought some from the motor shop in town for $10 per pencil size stick.
Tom at Helwig Carbon said that using pumice is not an ideal way to go but it does help with wearing the brushes in faster as well as removing burs, he also said that the clean copper of the commutator is higher friction and will run hotter then a commutator that has a film of graphite from the brushes and that letting the motor run at a low voltage with no load for a few days if possible is the best way to seat them in if you want to be assured that the motor will run cool and have long life.
SPRAYON Red Insulating Varnish, 20 oz. - Rubber Coatings and Insulating Varnish - 1D276|S00601000 - Grainger Industrial Supply