We can rebuild, Better than before.....
Well, as it turns out I didn't need to get to the LHS. A Google search for "Fowler flap hinges" turns up many sources, including this:
Scroll down the page and you'll see you can get the same gizmo for $6.70 US.
and
for a different commercial version.
and
has a home-made Fowler implementation on a Telemaster. Very cool.