The usual used parts sources - ebay, classifieds online and in print, salvage yards, bulletin boards like this...
But with the footpeg bracket being cast aluminum alloy, I can't picture it bending. If the peg doesn't sit level when deployed, I'd guess it's more likely the subframe is out of whack where the peg mounts, so I'd have a good look at the subframe and the tabs for the peg bracket for signs of it any bending.