Since the 425 is being phased out in favor of the 525 it might be hard to nail down a supplier. Rapids, mentioned in that thread, is pretty reputable but if you want the new 525s act quickly. Apparently there was a problem with the second production run and there may be a hiccup in the supply chain.
I will tell you the 525s are next to impossible to get right now. I have tried to get them from several different suppliers, but everyone seems to only have the 425s in stock right now.