Don, can you tell me how the clamp has failed? I've never seen the clamp itself fail, but sometimes the threads on the nut or bolt can strip -- HOPE that it's the sleeve nut, they should run ~ $30. Before you go and blow $250 , let me know what's wrong with yours - I may have the part you need floating around (for some reason, they don't sell the bolts but I try to salvage unavailable, or hard to come by, parts when I can

Please let me know where the problem is and I'll try to go without a huge outlay of $.