Don't know of any old junk yards that will just let a group of people wander around in.
But!
There is a used equipment sales place I have been wanting to stop at.
It's has a lot of cool looking, aged road tractors, earth moving stuff and farm equipment.
Not even out of your way.
When you leave Dad's Cafe, turn west on the outter road, it's about 2-1/2 miles and sets between the outer road and I-70.
Another mile west and you can jump back on I-70 at Danville, Mo.
Check out Google satilite, they have a lot more stuff now.

Don


1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!