If you're looking for a really neat switch to use as a fog light switch, use the rear window defrosted switch and knob from a VW Type II. It lights when in use, and if you remove the rubber "grip" and sand it lightly, then paint it, it looks like an ivory VW dash knob with a colored top.
Very neat, almost stock. I made one for the 356SC. If you want a pic of one all finished up, I can post it for you.
For a genuine Porsche "look", you can drill out any 356 knob, fit a small colored plastic gel into the hole on top and an VW emergency flasher knob "stem" into the bottom. Then use a VW emergency flasher switch without the flasher relay for a constant-on when the knob is pulled.
OR, sand down a '67 Type II emergency flasher knob to remove the white lettering on top. Use a paper punch to punch out a circle of masking tape and place it on top of the knob. Paint the knob cream, remove the masking tape and clear coat the knob. Again, use an emergency flasher switch without a relay for a constant-on lighted knob when pulled.
Lots of alternatives to spending that kind of coin., just gotta get your hands dirty.