I pre ordered my 5D MK II and got it in the first shipment. Canon has said they are making 7000 a month, so around 30,000 more or less could be distributed? We don't know how long they have been making them.
Many of the big retailers in the USA are not taking pre-orders, perhaps privately for good customers, but you can't pre-order from their website.
Amazon usually does not get the first batch of pro cameras, so pre-ordering with them is a losing cause.
I'm still waiting to find out more about how good it performs, it does not seem like there is anything urgent about me ordering it.