my dr office has always taken care of it, every 6 months i get a new one either in the mail or at my visit from them, i think they're getting them from the pharmacutical rep. and they bill insurance for it, my dr office people are great at all that kind of thing so i have no idea where to get them, i dunno maybe you could ask your pharmacist? the thought had never crossed my mind, and here in a year i have to switch from a pediatric center to an adult center so i guess i should start worrying about these things