I believe the whole thing is called the distribution block. The proportioning valve is integrated into the distribution block on most stock applications. I just replaced mine with an adjustable unit for when i have disks in the rear. To replace a stock one i would just go to a junk yard.
Here's the one i used if its of interest http://www.ssbrakes.com/commerce/det....cfm?nPID=8862
91 wrangler 4.0L, 4 in Suspension lift, 1 inch Shackle Lift, 1 inch Body Lift, 35" BFG Mud Terrains, Warn Rockcrawler Front Bumper, Hand Throttle, HiLift, 12 pack of Natty Boh.