Another great place to find mud flaps is ... the side of the road! I have picked up a few flaps laying on the side of the road. At my work, we tend to lose a flap now and then, and flaps aren't exactly cheap anymore. In fact, I have one from the road in the cab of my work truck now -- to remind me to put it on...
If different logo/designs/wording is a problem, just turn 'em around so the plain black side faces rearward,

The side of the road is also a good source for bungee cords ... Its amazing how many you see once you start looking ...
Eric, Normally for a post like that we'd send you a PM. But for THAT one, I'm afraid we're going to have to administer a severe beating.