Hi there! A fan after my own heart, bashing MacGyver and GI Joe together!

Rock gave me a heads up about your questions since I've been AWOL lately and maybe I can point you in the right direction. It sounds like you're looking to do a 12" (1/6) scale figure, right? Do you have the figure you're using already and just need the gear? Are you planning to alter the figure at all? I'm curious what you're going to use, especially for the head! If you want to and have a pic of the look you're going for, you can post it here or PM it to me and that might help me help you more.
Let me know for sure and I'll be able to gather some links for you to resources that might be helpful. To be honest, you're going to be better off buying the accessories you need piecemeal, rather than buying complete figures and then scavenging what you need. That can get expensive and then unless you plan to do more custom figures, you'll end up with a lot of stuff you'll never use.
I'm currently working on a 3.75 inch version of MacGyver from a GI Joe and the Mac in the Photobucket album is going to be reworked some, soon, I hope. That Mac is from a Sigma 6 GI Joe figure, which are about 8 inches tall and more anime/cartoonish. I imagine that's how Mac might look animated.

Since I finished him, I ordered a custom made jacket and so I want to make some modifications. I'm not sure if my source for that does 12" stuff or not, but it would be a great way to get pretty much exactly what you're looking for.
I know I probably have several threads for both Macs, as well as the Murdoc I did, but I'll have to take time later to find them for ya.
"It's amazing what one can do when one doesn't know what one can't do." Garfield the Cat
"Another day, a whole 'nother set of fresh possibilities. I'm a sucker for mornings." MacGyver