Question

how do I find caches with the partnership attribute?

Answer 1

Create a custom filter that limits the search to caches with the partnership attribute (this requires that you are a paying member of Project-GC) and then add this custom filter to just about any search on Project-GC. You create custom filters from the menu with your username on it, in the far right end of the menu bar.

Answer 2

Create a pocket query in Gecaching.com, specifying the partnership attribute. You can do 1000 caches in a pocket query, so perhaps try a large area, maybe the whole country. You do not not need to select a date to run. Instead, go to the Geocaching Map View, and in the Search pane select the pocket query you just created.