They hide in Europe, no species of grass snake in Texas.
Checkered garters and western ribbons should be pretty easy to find though. Look near water sources, slow moving streams, ponds, etc. Blacknecked garters are a bit more elusive, but they're around your area too I believe.
Blind snakes are a bit trickier, look under everything. They live in the mulch layer and most people would think they were an earth worm long before they'd ever think snake if they saw one. I'm not sure why you'd want one, what would you feed it? I can see going out and digging up fresh termite larvae now.
Ham