Need Help Sourcing a part.

Hi Folks,
Kinda new at this forum thing so, but im in a major pickle and need some help if you would be so kind.

I am in search of a Brake Proportioning Valve(hope i spelled it right) for a 1971 Demon. Its for my bosses car which is being totally restored but we are unable to source a replacement part for it. it needs to be an original unit.. So if anyone has one laying around or knows where i can get one please dont hesitate to shoot me a message.

Any and all leads would be much appreciated.

~Chuck