Where can I adopt a cecada turtle around the Austin area

We are actually looking for two to three turtles or tortoises (are those even the same thing?) to keep on our property to help keep the grass down in the back and also for pets to have. We have two acres, out in the hill country outside of the Austin Area. I am willing to drive to another city or area if I need to. We have a covered area outside to and plenty of space for them to raom around. The property is surrounded by an 8ft fence, so large wild animals, cyotes, deer,etc can get into the property. I have my name on one waiting list but the man doesn't get them in very often, the cecada's. We are looking for tortoises that are of the larger variety, so I guess they wouldn't have to be only cecadas as long as they are large turtles. Could you please help??
Thanks so much.