ProProsper doesn't make it trivial to extract the loan to listing pairing information. It is doable, however. Click on the "Query Analyzer" link in the Tools section of the menu on the left side (after you're logged in). Enter the query info below into the "SQL Statement" box.
loan.listingkey = listing.[key]
Press 'Run' to verify that it works properly, and then press 'Export CSV' to get all 9100+ loan/listing key pairs.