I picked up a milk crate full of them on the railroad tracks, they were all over by the loading dock back in like 65.
Also got my first speeding ticket at Lemon Park, 13 in a 5.
I was 13 on a Big Wheel.
Remember the Big T?

We had Hobby City so we bought slot cars and ran them on their tracks.
I used to get smaller gauge copper wire and would rewind the armatures on Mura motors.
You had to run heat sinks on the controllers to keep them from going up in smoke.
I had a few cars, Little Red Wagon, Hemi Under Glass, Invader Corvette and a few others.
We used to buy the parts and build our own cars.
Some of the old crew bought the tracks when Hobby City went under.

https://www.yelp.com/biz/buena-park-raceway-buena-park

My favorites:

Mr. Machine
Slot cars
Water rockets
Big Bang cannons
Daisy air rifles

You can still buy plastigoop, I wonder how hard it would be to turn a 5 dollar bottle of green into an 80 dollar dripping slime mod for your display?