I did some research regarding the availability of zombie heads in this thread if you are interested.
No you just asked Akky and I basically!

Yup a few of the more fleshy zed heads will do for T800's, T600's your probably better going for normal human heads with the eyes cleanly drilled out a touch, then tiny bits of plasti-rod/brass wire inserted to give it that 'rubber mask/skin job look'.
Anyway onto to the mototerminators:
Very nice indeed, remember to set one up on the lean and have the chainguns gyroscopically balanced, will make a nice looking mini that way. Remind me of the bike manufacturer again are they Void? (Kev White's old sculpts?).
The Commander