If you like the history of Derek Medding's ZERO-X there's a fascinating thread on FANDERSON's excellent public forum about model numbers and Century 21 modelshop sub-contractor Master Models. Have a look here. The Fanderson public forum is for all members of the public so be sure to have a look around the wider site and maybe contribute.
The discussion mentions the Zero-X model by Master Models, which you can see on their website here.
Be sure to check out all the Gerry Anderson models on Master Models' site in the sections titled FILM and TELEVISION in Gallery One.