A variation to Dan's suggestion would be that you could use a campaign that's triggered by "fills out form" and constraint "on page", then designate each webpage. This information could be stamped into a field as well so that you know the product interest.
Either way will work, the easiest one to set up will probably depend on which is easier: updating the 100+ URLs from all of their sources, or updating your triggers/flow steps for each product page.