Several of the branches in my area {Chicago burbs) are on the Comlink NXDN system. As such, there is no longer a license with First Student's name on it. All the users of the system are covered by Comlink's license. This would be true for just about any commercial trunked system. "End-user licensing" ended many years ago for these type of trunked systems. Our old frequencies, which were licenced to First Stundent, were basically surrendered to Comlink.
This days, searching the FCC database usually winds up being a bust. The best way I've found to find a lot of different businesses {Not just buses) is to monitor the local commercial trunked systems for active talkgroups and then start listening for clues. Good old fashioned radio detective work. Software like DSD+ can be extremely helpful in figuring out these wide-area, multiple-site trunked systems. Sometimes, you find some surprises too!