Don't know exactly what responses you were expecting for "amusement park style rolling stock" However, I will tell you that in addition to the Kennywood themed cars from MTH, Knoeble's Amusement Park has had a number of cars made for them, manufactured by Lionel and Weaver. Some of them are very hard to get. I've seen a Standard gauge car for Palisades Park, which is bright yellow. I don't know if an O gauge version exists, but would not be surprised either way.
For your viewing pleasure, here is a short video of 3 amusement park modules on the Lehigh Valley Hirailers layout. The operating accessories are from Lionel, Coaster Dynamics, and Mr. Christmas. BTW, I'm very found of the NS First Responders Training train.
Chris
LVHR