Wish I could help ya but those things are incredibly hard to find. I bought
mine (preassembled) years & years ago from "The edge company"... they ,of
course no longer sell them. If i had known how valuable they were going to
be I would have bought a bunch of em instead of just one! Seems that the
origional makers of the highway zapper were kindly threatened by the FCC
to stop making them.
Here is a pic of one you can use to post on other forums to aid in your
search.



And here is the one I own. It has seen much use over the years.

I had to modify the switch because I didnt like the pushbutton switch.

If the above pics dont work then just type in the url into your address
bar on your browser.

I wish you luck!