There's a gent in Canada who manufactures and sells them on e-Bay. There is an aluminum plug that fits into the road draft tube hole in the intake manifold with a PCV valve attached. A length of hose carries the fumes to the carb base. You have to devise your own means to access the intake manifold vacuum and install a hose connector thereto. These are obviously for the "late" flatheads - 8BA-8RT-8CM-etc.
Hope this helps.