Hello Tenchman, and welcome to the Thorn Cycling Forum!
I suggest you download and read the Thorn model brochures available here:
http://www.thorncycles.co.uk/models.htmlIn these brochures Thorn's designer, Andy Blance, carefully explains Thorn's preferences and design philosophy, which seems to be the opposite of what you are seeking -- steel frames, 26in/700C wheels and a choice of chain-driven derailleur or Rohloff drivetrains.
You said you...
...require a belt drive cycle for the bad roads here mainly sand /gravel/ashfelt/cement or just footpaths recommendations please realy want a 29 inch wheel with as wide tyre as poss 51 cm frame aluminum or carbon
Why not take a look at Thorn, read about the reasoning behind their design, and see if what is offered might meet your needs?
Perhaps one of Thorn's Rohloff-equipped models, equipped with a Hebie Chainglider to protect the chain from sand and the elements would work as well or better than what you are seeking. Well worth a look!
Best,
Dan.