Transactions and Tasks

For our return to vendor process, our customer service department is required to created a task to remind them to call the vendor to see if the item has been returned.  We create this task right off of the RA.   I am trying to create a saved search that will look at all the Return Authorizations and show which ones have this task associated with them and which ones don't.  That way I can be sure that our returns to vendors are being checked on and not falling through the cracks.
Any ideas?