I am the assistant coordinator for our local chapter of Project Linus, and I would be thrilled to death to meet a long arm quilter who was willing to help us out from time to time. Our members have various skill levels (and that's fine), so some quilts are quilted and some are tied and some are..some just are.
I would think you'd be able to donate your services without having to start a chapter. Have you checked the Project Linus website to see if there's a chapter near you? Plus, I think in Texas there is an offshoot called Linus Project?
I think it's great you want to help in this way!