If you really need one now I'd say just go out and buy a new one. They really aren't that expensive and you know that the new one will in fact work and won't be severly rusted out, bent or have other damage. Preifert makes a good headgate --- I haven't priced one in a long time but I bet you can get one in the $400 range.
If you have the luxury of time, then keep on trying to find a GOOD used one --- but first find out what new ones cost. Many's the time that I have observed people bidding on things at auctions and essentially paying retail prices for pretty well used and worn stuff, sometimes even in excess of retail!