There was a custom run of 50 caliber colt repros, I think walkers. I read somewhere that about 1,100 were made close to 1970 or 1980. One comes up on gun broker about once a year.
They were Dragoons though I don't remember which model. I remember them being for sale at the N-SSA Nationals from '76 on (possibly earlier, I wasn't there) for a few years. At that time a number of the sutlers were also importers and I think one of them had the run made up, at that time I knew who it was but can't remember.