You will likely need to place a wanted ad in the B&S forum for a C2/C3 HAIII head and either transfer the black teeth of the PD head over to the HAIII version, or see if there is a third party replacement. There is a thread in the B/S/T custom parts forum that is a feeler for M3 bezels in Ti, you might chime in for a request for a C2/C3 version.
Another way to obtain the head is to buy the C2 light and sell the body, lamp, and tailcap to recover most of your expense.
TnC products makes some surefire compatible heads, they may have a third party equivalent (not sure if they have a defender version).
You might venture over to the AR15.com forums and get the contact info for Brightflashlights, he/they have some misc SF parts available on occassion.