I have never heard of flanges not being accepted at quilt shows. Why would there be a restriction on them? If you have to ship the quilt, just be sure to pack it so that the flange won't be pressed out of shape in the box.
Edited - I put a flange on this quilt -
http://www.quiltingboard.com/picture...d-t211129.html - it's the green piece set on point around the light tan.