The new Pentax DA 560mm f/5.6 ED AW lens is now in stock and shipping. The 560mm lens is equivalent to an 859mm lens on Pentax DSLRs thanks to the crop factor of their APS-C sensors. Check it out here at B&H or Adorama.
It also appears to be in stock in the Sony mount option here at Adorama. Note that the Sony version does not include Optical Stabilization due to the built-in stabilization in Sony Alpha cameras; however, Sigma still prices the Sony mount version at the same price of the other OS versions.