Pretty much any of the Mustang parts houses
NPD, Mustang Depot, etc.
I picked up a nice Maier Racing adjustable unit from Mustang Depot. Very nice piece although it wasn't packaged very well in the box and had some damage that I have to fix.
So you might want to ask them to pack it carefully if you aren't going to repaint it.
sometimes I think these people could care less once they get their cash.
On the other hand NPD has been the best when it comes to shipping stuff.
Good luck,
Scott