If you do not have any exotic animals stores in your area, your best bet would be to look through the classified ads. You can also try looking online as well. Maybe even asking a local animal shelter when you could purchase a sugar glider in San Antonio. http://www.petclassifieds.us/c/1639/Sugar-Gliders.html
Be prepared for a ton of work and do lots of research so you know what you are getting in to. I have one and she is a sweetie but like I mentioned it's a lot of work. They require a lot of time and expensive diets.