The air cylinder he is talking about is on the coach, not the toad, as is the SMI and M&G cylinders the other mentioned. This type of cylinder is used as an air reservoir on the coach when the coach has air over hydraulic brake system, so it could be most any brand.
Since the air line to the quick connect is NOT pressure regulated by the coach brake system, it would have to be a toad brake that uses coach air but is triggered by an electrical hook-up, typically to the coach brake lights, or an inertial switch. Both SMI and M&G would qualify for that, but so would some others. You could use any toa d brake that requires a constant air pressure source. That leaves out Brake Buddy and Brakemaster.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL