What MTB 10 speed double cranksets exist with 180mm cranks? I am looking for a a 10 speed dual crankset that has 180mm cranks.

I see the SRAM cranksets only come in 170 and 175mm.
http://bike.shimano.com/publish/content/global_cycle/en/us/index/products/mountain/new_xtr/component_systems/race.html#drivetrain/0001/FC-M985

Hopefully that links you to the XTR Race crankset. Double and available in 180mm. 
Then new XT Dyna-sys cranksets, in triple, will also be available in 180mm.