Beautiful garter!!! Scenting the mice should work well for you, it just may take a while. If you're feeding live fish, you can put some pinkies in with the fish, and often the snake will grab for a fish, hit a pink instead, and down it. But give him some time to settle in, he may have had a traumatic couple of weeks if he was handled too much by kids.

Here's a general care sheet if you need a refresher...
http://www.thamnophis.com/caresheets...ake_Care_Sheet

Keep us posted!!