Rather than leave a big, ugly hole, why not just apply a little JB Weld over it?
Once upon a time the key was that the last plate in the cylinder held the cylinder in the shaft, so that if you could get a thin hook-like device (sort of like the hooked nail file on a small pocket knife, which are too thick nowdays
) into the slot all the way to the end, and hook the last plate, the whole thing would just slide right out.
A local locksmith could probably help you out in short order.
