The disc parking brake in the driveline was I believe optional, or came on some trucks depending on other equipment.
They were made by Tru-Stop and used in many different brands of trucks for many many years. Mostly stopped being used when trucks with air brakes were equipped with the (then new) spring parking brake chambers.
The present company supporting Tru-Stop brakes is Stockbridge Engineering in Stockbridge, WI. They still make parking brakes, but also use them to control cable drums like for stringing power lines.
http://www.stockbridgeengineering.com/products/It's also very likely normal brake and clutch shops can reline your old shoes, or talk to Stockbridge.
Attached is a service manual for the Tru-Stop brake.
