Comes from 'scubus' (pronounced scubas) which comes from school bus.
Scubillion is a large amount of school buses located in one relative area. Also, a large amount of yellow/orange cars located closely together.
Used in the count "The School Bus" game when one is passing by a bus station with many busses visable.
"Look, I found the scubillion!"
"Look at that parking lot! It's a scubillion!"