Mostly through wholesalers. They try to get chams from some breeders but they require the breeder to be able to supply all their locations within a general area.
I was contact by their head office about two years ago. They wanted me to be able to supply all their locations here in Canada and only be exclusive to them. I could not commit to the contract. If something went wrong and we were unable to supply the number of chams they were looking for by a deadline, they could then sue. It might be different in the US, but was just not worth the risk here.