Vendor Name is now available in Add Columns in Items Search to help view and sort. Here's a way to find all Items that have a Vendor assigned--useful for automatic PO's.
Go to Items Search, Find All, click Add (+) on header row, and choose Vendor Name. This will add Vendor Name as a Column. Click Vendor Name column header to sort.
Right-click the Filter box above Vendor Name and choose # Not Equal To and Tab out. This will reduce the Items Search results to those "not equal to" blank for this Column.