Have you looked into Cleaview School? They are a Sudbury model school in Austin. Good luck in your search!
Jen - Partner to Joe, Craig, & Jordan , mama to DS1 (7/13/99), DS2 (10/27/01), and DS3 (6/13/06), and DS4 born 12/13/12! Attachment Parent, co-sleeper, baby-wearer, Sudbury School founder & educator, PhD Candidate doing birth research, cloth diaper lover, GF (again), etc!