Re: 1964 Johnson 40hp electric shift parts
Although I haven't yet dealt with them personally, they do appear to carry a good array of parts for old outboards. I will likely give them a call myself for some of the harder to find parts for my 1958 Johnson.
Try
Laings Outboards for what you seek.
Those electric shift 40s were deluxe rigs in their day, but a lot of people are scared of them because of hard to find lower unit parts and the need for special lower unit gear oil (be aware of that one). Although many would say they are archaic, I like the old large displacement 40s. They pulled hard from idle and are a well-proven darn good outboard motor. They were sold as heavy duty workhorse motors in some parts of the world until around 1990 as far as I know. The last regular production 40s were the 1976 models, although the last go for the Electramatic (or Selectric as Evinrude called them) was 1970.
Let us know how you make out in the future, and good luck!