Actually, it really doesn't matter where you get them, if mice or any rodent is living together with other rodents of the same species, they will get parasites. With all of the poop and sharing of food and all of that, it's inevitable. I talked to my teacher, the vet, and he said that the parasites the mice have won't transmit to the snakes. It's not really possibly since the parasites in the mice are usually host-specific, meaning they can only live in mice, and they aren't in the right stage of development to infect anything, since the parasites are still in the mouse.