Aristocob has MM stems for 50 cents. Mars has stems for 75 cents and very good prices on cobs. mars cigars & pipes - Corncob
I usually get the stems when I'm ordering more cobs and I liked dealing with MM. I was able to buy natural finished Diplomats via the factory. ASFAIK, these were never listed on their website. I also got several "Morgans" which were prototypes that had a natural finish. The natural's smoke better for me than the plaster finished pipes. The Missouri Prides are naturals and good smokers, as well.
I have yet to replace a stem due to breakage or chewing through a stem.