Ah! You are in Canada. I'm not sure if you can get Provent-A-Mite shipped up there. Hopefully someone with Jurrasimite experience will get on in a bit.
The thing about mites is that they don't stay in the enclosure. So if an animal in a pet store gets mites then they can be on just about anything, and since most reptile supplies are kept in close proximity to the animals, I think that is a most likely way of them getting into your home...