Ok, so the brain has been on overdrive thinking about Mad Max and gaming possibilities. Whilst I like the look of Devil's Run: Route 666 it is 20mm scale, so vehicles like tankers will be a tad big (also the game isn't due for delivery until February next year). The one thing that struck me about Mad Max Fury Road was the scale of evereything. The desert, the fleets of gang vehicles, these weren't battles with one or two vehicles, but potentially dozens a side.
I had a Eureka! moment on the train today when I recalled TimeCast sell sets of 1/300th plastic modern cars, twenty in a pack for just £2.50. This would mean they are easy to convert and you can have a lot of them. They would also be compatible with 1/300th WW2 and Modern vehicles form the likes of GHQ and Heroics & Ros, so lots opportunities for bits and spares.
The TimeCast models are (I guess) architects models for the lovely white building models you see of planned constructions, so I am hoping there might be more vehicles out "there" that I can hunt down. And of course, there are the Irregular 'Mad Ron' vehicles which can also join the fray...
Edit. Or you can buy 1/300th 100 cars for £3.61 with free postage from China on eBay!