Red maple doesn't generally do well in alkaline soil in Austin. Try shantung maple instead but if you really want the red fall color, you'll have to drive to south Ft Worth to get 'Fire Dragon' shantung maple at Metro Maples. Otherwise Natural Gardener nursery in Austin has regular shantung maple that typically produce bright yellow fall color.

If you still want to try Red maple anyway, try Lowe's or Home Depot. I always see them up here but not sure if Austin big box stores carry sell them.

I'm in Austin. If you want a larger tree try a Bigtooth maple or a Shantung Maple. The Fire Dragon does really well. I've had luck finding Bigtooth at Countryside Nursery in North austin. You may also try Redbarn, Great Outdoors, and Natural Gardener.

If you want Japanese maple, you can try Lowes. I've seen some emperor's and Tamukeyama's in stock. Great outdoors also carries some great Japanese maples.