While I was doing some searches for relevant places to link to, I came across these interesting finds...
One of the Gottman Toys 1/16 size DirtSlingers on Ebay
A custom 1/64th size DirtSlinger on Ebay
The real Dirt Challenger may be in the process of being parted out, but you can own a 1/64th version of it for around $20-$30 on Ebay
And how about this blast-from-the-past... a story from 1988 in the Chicago Tribune about the tractor pulls at the Illinois State Fair. Bill Leischner is heavily quoted in it!