Austin can be described as 266 sqare miles surrounded by reality. Still, it has its advantages. THe primary advantage is the proximity to Lake Travis. wet-willie listed the the better land access dive spots.
wet-willie's link for dive shops didn't work for me. The main dive shops are:
North: Deep Blue Scuba, Scubaland Adventures
Central: Austin Aqua Sports, Tom's Dive and Ski
South: Oak Hill Scuba, Scubaland Adventures
Northwest: Dive World
Any of these shops can hook you up with tanks and any other gear that you might need. I'm at Oak Hill Scuba weekdays after four except all day on Wednesdays. Shoot me a PM if you can't find a buddy and I'll try to hook you up with one of my divers.
Mack