I have a '59 with the same problem. Luckily, the previous owner cut away the rust and applied some sort of brown translucent rust inhibitor to the remaining metal. He didn't attempt a patch, just left the holes.
I, however, am not so smart. For less than the cost of a professional repair, I have purchased a little Lincoln home / farm welder and will attempt a repair myself. I have since discovered that I should purchase the MIG accessory pack and practice that for a bit first.
BTW a guy here in Seattle, had an ad in the paper for two "perfect" 1958 fenders. He was asking $1,200 or best offer. I didn't call. Keep me posted on your travails.
