Ebay is your best bet and you should be able to get a good deal. There's at least one up for auction right now. The Snow-Troll is definitely worth tracking down, I won't be parting with mine anytime soon.
If WETA release a couple more Trolls then this will always be the elusive one to get I think. The CT on it's own is a great piece, but if there are a couple more breeds of Troll to add then that would give ST a big boost as he has definately been made in line with WETA's visions.