They look like a common fiberglass flare, except that they've been arched at the top of the rears. You could use some BroncoDesign flares, if Brian will sell you the one you need, and nobody would notice that your driver's side didn't have the arch, and your passenger side did.
I have a spare rear, just need to see if it's passenger or driver. Confirmed it's for the driver's side. You want to see a pic of what they look like on my truck?
http://i164.photobucket.com/albums/u27/cbarronj/croproof.jpg
http://i164.photobucket.com/albums/u27/cbarronj/Top1.jpg
I'll let you have it for the cost of shipping. Mike, at BroncoDesigns sent me replacements because it got slightly knicked in transit the first time, very minor, but I'd never worked with glass before, and he insisted on sending me out replacements. I couldn't turn around and charge for it, and it would be one less thing the warden could bitch about.
EDIT: After seeing the Wildhorses flare, that looks almost exactly like what you have. Not much of a difference in the BroncoDesign flares, but if you want to be spot on, buy a pair of the WH.