Hi Spiker32 and welcome to the forums.
You might find you get a better answer if you add a new post in the chassis section, as the title of this one doesn't really describe your question.
It's unlikely many Fugitive owners would have a set of plans unless they'd reverse engineered them, the Fugs came as either a complete frame or as a kit of frame parts to be welded together.
Frames or project cars come up fairly frequently on ebay or the for sale area on here, and I believe Kingfisher Kustoms also still have their Commando frames available new. Billy Bobs Buggy's at
http://billybobsbuggyshop.co.uk/ also supply new sandrail frames.
If you really want to go the build your own frame route then there's plenty of people selling (non Fugitive) Sandrail plans - ebay's a reasonable start point for these but I couldn't vouch for the quality of these.
Cheers
Paul.