Sk Grimes can fashion a custom lens cap I believe at one time they also made shades as well.
Rumor has it that this camera was made by Mamiya for the Japanese owners of the Plauble name.
You may want try a rubber shade until you can get down to NY to try the shades that BH Sells. They are none too sexy, but effective. I hear there is a huge camera store in Boston, somewhat closer to you, called Loenstien and somebody (not too helpful, but maybe another member can help with the name) that may have what you are looking for in the way of a shade or generic lens cap.
In the back of this store is a camera repair counter (also calling themselves SK Grimes-- or so I am told) and they may be able to address the RF issue.
I have thought long and hard about the 67w (same camera 55mm nikkor lens), but the fact it hasn't been made in close to 15 years, the mixed heritage and rarity making quality repairs and parts rarer still caused me to look elsewhere.