Garter Care

Hi, I just have a few questions about garter snake care:D
1. I live in a place where they are native ( well, they are native in most places ), so would I need to heat the tank in the warmer months ?
2. Is a heat mat or UTH better
3. Where is a good place to buy garter snakes ?

I give mine belly heat at 85*F year round. Mine are not kept in the "snake room" with the BP's and BCI's, they are in a cooler room in the house.

I've never seen one in my local exotic store, mine was found injured in the garage.