I've decided the 52-47-34 gearing on my Miyata 610 is just not working that great for me. Does anyone know of a decent source for old chainrings outside of eBay? I'd prefer to swap out the 47 with something in the 39-42 range, and if I am really lucky bring the 52 down to a 50, but I can't find much (or anything) in the size I need. According to Sheldon Brown's site, I am looking for a "Stronglight 80, 99, 100, some SR triples. (Obsolete)", with a 50.5 nearest/81.8 non-adjacent spacing. Makes sense, since it is an SR triple. I'm not reassured by that obsolete marking...

Or, am I better off to just go find a new square taper crank in a gearing I like? Are all square tapers the same size?