The "Tagging" trick Mike teaches does not work on AWeber generated landing pages. What Is the solution?

YES; the tagging feature does not work on AWeber landing pages as it breaks their landing page. What you can alternatively do is duplicate the page for each vendor you decide to get traffic from. And then you can tag the optin form itself on your landing page with the vendor's name.

So then when you search for the name in subscribers; you know which vendor generated which leads for you through their traffic,

Checkout diagram below for clarity: