Just dug out my drawings, finding the combined sprag clutch and chain sprocket is not going to be easy.
If I were going to make the kick starter then I think I would make shaft #24 from 3/8" silver steel and reduce the end down to 1/4" to fit the small gear and bearing. On the other end a 3/8ID x 5/8 OD sprag clutch will run on the now 3/8" shaft. Fit the sprag clutch into a cup shaped housing with the end tapped with a ring of holes so that a sprocket with matching hole PCD can be screwed onto the end. If you are not sure of this shout and I'll sketch something out.
This will in effect form a part like the one shown but with no need for the 1/4" shaft extension.
Edit, the part in question is the second one down just in case anyone knows of a similar UK item
Edited By JasonB on 24/08/2021 14:38:18