Have you tried contacting any brake manufacturers? Bendix has helped a company I worked for on motorhomes a few years ago. You could try contacting them and see if they have any suggestions. Here's from their website.
For technical support, call 1-800-AIR-BRAKE
(1-800-247-2725), Monday through Friday, 8:00 a.m. to 6:00 p.m. EST, and follow the instructions in the recorded message.
Or, you may e-mail the Bendix Tech Team at TechTeam@bendix.com