you can find the old or new optimus prime's (3 versions) at www.freewebs.com/paper-toys. Hope this helps. (i sort of seen that this thread is old, but it might still help. :-D )
counting the cube stuff I have 13 different Optimus Prime models on my drive... and there are still others that I haven't bothered to collect cause they are too "designer" for my tastes.. lol
Yeah; I have a few on my computer as well. I was going to translate them onto sheet styrene and see about building them that way, but never got around to it.
paper-replika.com provides 2 models. Simple and complex. I have build the simple one and the complex one is waiting until i have enough time and courage.....
For those interested in Optimus Prime models, I recently came across this paper version of the Masterpiece OP toy. I think it stands about 24cm in robot mode when completed and it transforms from bot to truck. Also includes the trailer.
Requires colored card stock though so I'm planning on doing a "skinned" version of it. Likely in Original, Magnus and Nemesis flavors.