Hi and welcome. Cool bus!
Per identifying it, I'm assuming you've scoured it for plaques and such identifying it in some manner?
You should be able to also find information on the axels, transmission and engine. That won't tell you the body manufacturer, but it might lead you in the right direction. Save all that identification information once you find it. You'll use it sometime later!
Hopefully someone on here will simply reply and say..."Oh, that's a blah blah blah".