MTH actually sells diecast autos. They're an accessory item, featured in their annual Ready-To-Run catalog. I'm looking at the 2015 catalog...the cars are shown on page 40, item 30-50066. I'm sure they used one of this type, or similar from the same supplier, for their animated accessories.
That said, I know you'd be less than thrilled to have to buy the whole MTH set of 32 cars at $229.95 to get one for your station!! However, MTH dealers (like us) sell them individually...that'll be the easy part. Do the math....they're not expensive individually at all.
Then you're going to have to find/make a 'shoe' to attach to the bottom of the car that will engage the floor mechanism. That's where Midge (MTH-Parts) may be able to help....worth a call, anyway.
I don't happen to have the accessory handy to give you any further info. But, knowing how helpful the forumites are, I'm sure more data is forthcoming.
Stay tuned!