It looks like that one is actually one of Opal's Rainforest colors. Here's the only thing I found:
http://cgi.ebay.com/OPAL-4ply-SOCK-Y...3286.m63.l1177
It's from Britain, but might be your only option. I know they have colors that they sell on a limited basis, so it might be one of the discontinued ones.
Someone else on Ravelry has a skein for sale of something that looks like a really similar colorway:
http://www.ravelry.com/people/tilatu...d---rainforest
Good luck!