Proportioning valve...

...for a 72 scamp with a 8 1/4 rear out of a 74 dart and a set of Kelsy Hayse disks up front. Is there anyone that makes a new valve (anyone know a part number) or do I have to scrounge the yards (anyone have one for sale)?
Also looking for a nonpower master cylinder for the same car. I asked the kid at the local Shmucks Auto Parts and he just looked at me funny and said that the computer didn't show one.