Many have been waiting for quite some time to upgrade their Socket F systems with AMD's Istanbul six-core Opterons and it looks like they are finally available.
For those in Japan, it looks like AKIBA PC Hotline has spotted a few in the wild on retail shelves. If you're not lucky enough to find one on the shelves near you, they are available online as well. Newegg has a few of them, but sadly they don't seem to have 2.6GHz Opteron 2435 available.
Istanbul is AMD's drop-in upgrade for the current Shanghai Opterons. AMD's gone with a 6MB L3 cache and a 45nm chip while adding two more cores for Socket F systems as well. Right now only the 2.2GHz, 2.4GHz, and 2.6GHz Opterons are available but AMD should be bringing more to the market soon.