Jack,
you would be surprised how much armour there is in the UK, how many owners would be interested in bringing it out to an event is another issue!
I would certainly be up for it and can think of several others who would be too. The main problem would be, as always, cost. For instance, to attend and partake in such an event in the midlands would cost me in the region of £1500 to £2000, the vast majority of it on transport. That's a huge sum for a weekend playing.
Fuel sponsorship for the tanks is a possibility but is actually a small part of the overall cost.
With the right venue and mix of on/off road running, an event of this sort would be brilliant.
Go for it!