This comes from canonrumors:
Canon Canada has started to confirm the preorder lists from retailers for the EOS-1D X. Retailers have to prove the people buying the camera are CPS members, and have prepaid for the camera. If the camera is needed for the Olympics, it appears you’re moved to the front of the line. I don’t know if any other countries are going to experience the same limitations with the initial shipment of cameras.
Canon Canada expects a very small number of cameras in July, and that should be the same across the globe.
Moreover, CR suggests that the EOS-1D X will not start to ship regularly before August-September 2012.