Agreed, I love my old 2 stroke small outboards, and don't want to change them for a modern 4 stroke for what we use them for. I do my best to keep them running, but the cost of some of the new parts is such that it's just not worth it, so I end up waiting until the right part comes up at the right price.
Check the 4 hp parts with the online diagrams/parts finders, but quite likely to share parts with an Evinrude.
I have a 5 hp Johnson and 9.9 hp Johnson that we use on an aluminium run around, and both share parts with their equivalent vintage Evinrudes. I recently bought a whole lower gear box for the 5hp, and whilst it had a very slightly different shape gear selector rod as it was a different model year, managed to reprofile it to fit. Keep an eye on Ebay and quite possibly the part will turn up soon, or phone a few of the firm breaking this type of engine on Ebay.