your wheels you posted in the for sale section are "series II" go powers so the sprocket is not hard to find :thumbsup: All you need is a 3.25" bolt circle sprocket NOT the nearly unobtainable 3 stud go power sprocket. There is a regular seller on ebay that sells NOS bendix sprockets usually with a low starting bid in both 60 and 72 tooth count, and a 5" Bendix brake can be bought direct from allied leisure that is workable with the right spacer. Or you could go with probably just about any Universal brake/sprocket setup that has the 3.25 pattern in it.
Good luck