I have one like you're talking about, basically a big rectanglar frame with a pipe that goes down thru the roll, then has an arm that pivots around and clamps the wire at the back, held tight by 3 cam buckles. Don't have any pictures off hand but if you're interested I can try to take a couple this weekend. Mine came from a local high-school, they were selling them for $250. Works ok.
Neighbor made an unroller by removing the auger from his post digger and attaching a piece of pipe with a plate under the roll, unrolls it with that and uses a wooden stretcher on it, cheap and works.
cfpinz