I remember it took quite long that the 5DMkII was really available. But maybe Canon calculated the demand of the market better for the 60D (not that easy for the first plastic-xxD with articulating screen ).
50D was announced on August the 26th of 2008 (Please note the date
) and was delivered to the stores on October the 6th in the USA. Early November was fully available in the average european store.
I don't think there's gonna be much supply problem with this camera. 5DMkII was a different case, because production is WAY lower. If you look for the highest end, problems are much worse. Just try to buy a nikon D3s
This kind of camera sell like hotcakes, so production has higher volumes, and therefore has normally no major shortages. Specially if they use 550D/7D technology on this one which is likely.