I have a few complete colt m16 lw front sight bases with bayonet lugs they are a hit and miss on fit though since they are drilled deeper than the cilvilian sporters but match horizontally but if you have a jig or if having it sent to a smith like KKF i'm sure they can be made to fit.
$25 ea. shipped.
Also shown DPMS hbar front sight post. $29 shipped