Hi, read about your problem with not being able to evolve into Froslass. I know it is a Dawn Stone evolution, but obviously it didn't exist until Generation IV. Are you sure you've covered every single possible in-game trade available? So far I seem to find one in every major city (except maybe Esmereld, where we got Eevee's Egg).
I'm doing a walkthrough for the game, meanwhile. If I ever locate it, I can tell you. However, I think I've thought up an elegant solution should there indeed be no wild appearance of it in-game, and it could be a change in a future beta. The only problem is it could result in a male, which doesn't exist...so I would hope the in-game trade is there somewhere instead, or add another "legendary event" somewhere in a winter area (Route or cavern).