I got mine on Ebay. It was the cheapest I could find and they worked great! They got me out 9 miles on Erie last year without a problem!
One thing though, if you are pulling a sled with a rope...don't hit the breaks and then take off again. My chains grabbed the tow rope on a two man fish trap and proceeded to coil it up and slam the shanty into the hitch and rear end causing some damage!