Check www.dspracing.com, not sure if they make one for the kdx, but I did buy their widest pegs on the market for a CR, will never go back to stock pegs.
What David Trustrum has done, is cut an old footpeg in half, then weld half each to the pegs, thereby widening them. Just make sure you get someone who knows what they're doing with a welder tho ;)
Go to Canadian Dave's website and look in the Fredette Racing section, they are very reasonably priced. they fit 84-93, but I bet if you call him, he may have some for newer bikes www.justkdx.dirtrider.net I believe.