Does anyone know where I can find aftermarket foot pegs for my 400ex?

 

you could go AC Racing pro pegs. That would give you nerfs to.

 

I just made my own, made them an inch wider toward the back and put a 35 degree up turn on the end. I used 1/8" x 1 1/4" flat steel. I could tell the difference this past weekend at the race.
Also, I cut the grooves in where they would hold my feet now. It gives a much better feel than the thin factory ones. I feel more stable.