Snake mites, Ophionyssus natricis, are found on snakes (and occasionally lizards) and don't live long without a host. They're not native to North America. You can't go outside and pick one up on your shoe, or at a garden center. You could potentially pick one up at a pet store that stocks live reptiles, or at a show, or from bringing a new animal into your collection. There's also a small chance of them hitching a ride on live rats, I've heard.
NightWolf, I wouldn't worry too much about some stray bugs. They won't do any harm and you'll probably get them all on your next clean. If you wanna sterilize the wood hide, you can bake it at low heat in the oven for about half an hour.