score:3
Yes, website that reference those codes do exist. CouponsHelper is an example.
Better than referring to a website, I suggest installing the CouponsHelper extension if you use Firefox as your web browser.
Basically, every time you come across a website that has coupon number entry, a prompt appears on the top of the browser with known working coupon numbers for that website. It works with various retailers, including travel-related services. For instance, codes are suggested when booking a ticket on the French railways website.