Top level menu item link not to page or post?

I am full of questions today – My client likes to have the “buy” button in his main navigation link, not to a specific page, but to a “search result” which shows all the products on his site. Is there a way to have a top level navigation item link to something like:

https://www.sparrowtraps.net/cgi-bin/shopper.cgi?search=action&keywords=all

which is not a page per se, but a function of the shopping cart software?