Hi Glen,
Garters, in general, are known to be very calm, and they rarely bite. The wild caught ones are more likely to bite, but even then, they bluff more often than bite. If you buy just about any captive born specimen, it is more likely to be even more docile and friendly than a wild caught one.
I think the smallest species is atratus. I am no exp3rt but I heard somewhere that they were. And I agree with Cazador, my snake is calm unless you are holding it or make sudden movements while it's looking at you (it's wildcaught)
Shortheaded garters are someof the smallest, tho hard to come by. Most garters are fairly calm. You can get a male of any species, they tend to be smaller than the females.
smaller garters that should be available are: shortheads, butlers, ordinoides.
Perhaps it´s an alternative for you to gain some informations about brownsnakes. Very interesting snakes and they mostly stay smaller than 30 to 40 cm. But they are specialized in worms as food.
Hi again Glen,
Since there are so many species and subspecies of garters, I'd suggest looking at pictures online. See which ones you find the most interesting/beautiful, and then ask about the size of that particular species or subspecies. Thamnophis made an incredible website that conveniently shows each one very clearly (Kousebandslangen.nl).