That's one possible aspect I suppose, but they don't seem to have any trouble getting most other reptiles imported. What few garters come in, seem to be "trash" if you will, just thrown in with all the pythons and such for import.

You can try to sell the "I think who ever brought in various garters to the UK could make a LOT of money if they took the risk of importing them." to someone in the UK who wishes to bother. Show me one person that wants to pay to ship a bunch of really quality garters even if charged nothing for the snakes themselves. Nobody wants to do it for whatever reason.