Auto-select work items assigned to vendor when creating a purchase order

If my project consists of work items from say, 4 different vendors, I usually create a purchase order for each vendor.  However, when creating a report, you cannot see which vendor the work item is assigned to, and selecting an item from there will offer to change its assigned vendor.  When creating a purchase order report, I would like a "vendor" column in the work items list so I can see which items I need to select for that vendor.  Or add an item set for "Items assigned to this vendor."  Better yet, checkbox all the items assigned to that vendor for me when I select the vendor.