Mechanical Brake linkage on Mk IV Saloon

I’m searching for a source for the small, threaded pin that screws into the yoke on the mechanical brake linkage on a 1948 Mk IV. The pin creates the pivot point that links the rod sections to another pivot, or in this case, the handbrake to the rod to actuate the rear brakes. It’s been lost over the years. One end is threaded, and the other end is much smaller, drilled to accept a split pin. Thank you.

Mine is probably different but similar.

I think you are looking for what is called a shoulder bolt.
The end with the hex head is the shoulder, perhaps 3/8" diameter.
The other end is threaded, probably 1/4" BSF thread, with a hole for the split cotter pin.
They are specified by shoulder diameter and length of shoulder.
McMaster-Carr sells them in SAE inch sizes, but not with BSF thread nor a split cotter pin hole. But it would be good enough to get you by.