Hi, A company called Character Options, Ltd. of the UK (actually manufactured in China) produced the recent Dr. Who figures. Their website is:
http://www.character-online.com/, they are distributed in the US by Underground Toys of California. They have produced the 12" Cybermen used in the current series, as you say you already are aware. These are very hard to come by, if at all. You may want to sign up for updates on new products or write Character Options customer service department directly to find out about any possibility of a Cyberman from the years you mentioned.
There is a 9" talking figure of a "Black Cybertrooper", which is the basic Cyberman in black, and a classic silver one. Produced by Unusual Collectibles, they're available online. Looking at the crude bash-it-together nature of the Cyberman you want to create I really don't think it would be that difficult to scratch build one yourself. You can easily form the face from Sculpey or even just plastic pieces. Just glue plastic shapes over a "face" for eye brows, nose and mouth; cut a couple of holes for eyes and back with opaque plastic, cut a another hole for the mouth opening. Make the finned sides of the helmet by gluing together plastic card with thinner card between each "fin" (like making a radiator), then when dry sand the whole thing to shape or you can cut each piece to shape before assembly. The breast plate and other items on the costume look very basic and simple to again sculpt in Sculpey or to piece together from scraps of plastic card and bits and pieces from around the house, hardware and automotive stores. There are GI Joe silver boots that would work very well as the Cyber-boots.
Thought you may get a kick out of this poster, done after the "Reservoir Dogs" poster called "Reservoir Bots":
