The B-Series bus became a staple at bus stops starting in the 1960's. The engineering of these buses closely resembled that of General Motors trucks from the same period.
Early models of this bus came with three engine options. They were the gasoline V6, diesel V6, and gasoline inline 6. These engines ranged from 5.7L up to 7.0L. A diesel 8.2L V8 came later on, along with a turbocharged engine for buses that needed to get kids to school in a hurry.
Little changes were made to these buses over the years, and when they did make changes they were usually years behind the General Motors trucks that the engineering was borrowed from.
General Motors sabotaged its dominating share of the school bus market when they decided to sign an exclusive deal with Bluebird, making Bluebird the only body manufacturer on new B-series buses. They would make the B-series chassis into the CV200, although they also offered this model with a Navistar-International and Freightliner chassis. It was an open relationship, but only for Bluebird.
There are plenty of used B-series buses for sale out there, but chances are you won't find them in your local used car classifieds. I guess the bus companies think the general public has no interest in buying used school buses. The easiest place to buy one of these buses is on eBay. There are usually dozens of listings for them, along with hundreds of listings for parts. Some bus companies will sell off their buses exclusively on eBay to avoid the costs and time involved with selling them using conventional methods.