GL1500 Goldwing alternators work just fine if you re-clock them (take out the three screws holding the case halves together and spin the housings -- you'll see when you lay it beside a Valk alt). They are cheaper from Honda and from eBay. You might also try Ken Heming at M.A.R.S., though I don't recall what his prices are:
http://mysite.ncnetwork.net/resp3jbj/