DART has a fleet of about 470+ NABI CNG buses, along with some New Flyer XN40s, some ARBOC Spirit of Mobility for feeder routes, and 7 Proterra BE35s that run on the 749 line to the Convention Center. I missed out on the last diesel bus by about a year, and unfortunately the RTS by some more.
Northwest Bus Maintenance, as visible from the Orange Line:
A quick shot of a NABI 60-BRT CNG from Fort Worth Trinity Metro:
ElDorado buses running at DFW Airport, run by ABM Aviation: