Howdy and welcome to the forum. It's always good to hear from seasoned herpetculturist who are now also getting into Thamnophis. I do find it funny though how you live in Oregon and your first garter was a Fla. blue T.s.sirtalis, considering the large variety of beautiful garters that live right around you.
I think I'd be out every warm day looking for T.s.concinnus, T.s.fitchi and T.ordinoides.....not to mention hitting CA for some T.s.infernalis and T.e.terrestris. Here in PA we've got T.s.sirtalis and then there's T.s.sirtalis and I think I've seen some T.s.sirtalis! Ok yeh, there are T.butleri and T.brachystoma, but compared to a bright blue T.s.infernalis?....yeh, you get the point.
Roy