I think you can get them from Last Refuge with the hinges for $275. He might sell you one without hinges.
Skip, I have heard a ton of conflicting info for Last Refuge, but overall the reviews of the beds (and tailgates) have been good. their main problem product seems to be the RPU body. Good luck buddy
What you might be looking for is a 37 tailgate. Same size as the 32 thru 36 but no straps. It uses the modern method of mounting; a small bolt on bracket at each bottom corner. They work great on the 32 bed. I've done it twice. I just happen to have a new repro one set up for no chains that's taking up space in my barn. What ever they are going for now I will do two thirds, just so I don't have to trip over it again.
37 Gate works nice, go for it! RPU Bodies have come a long way since they were first introduced, Any one can PM me for the nearest one to thier location so they can see for themselves.
Last Refuge, that's what I have on mine, all went well, the only issue was that they were a bit slow to ship! Good Luck!