You can only search by Co-Operating Brokerage for unavailable properties.
Select Search and change the Availability filter to Unavailable and deselect Available.
The Co-Operating Brokerage filter can be added by scrolling to the end of the filters and choosing the Add a Field drop down.
1. Click on Filters or More Filters (depending on your layout view) to access all available Search Filters.
2. Scroll to the bottom of the Filters.
3. Click the Add a Field drop down menu, or select the Suggestions icon
4. Select Co-Operating Brokerage from the drop down.
5. The Co-Operating Brokerage field will be available in the list of available filters, and you can now add the Brokerage Name in the text box