Can the PO Receipt Number be included as a journal entry Supporting References?

For the SLA Event Class, Receipt into Receiving Inspection, we have set up Supporting Refences to record the Inventory Item#, PO#,  Receipt Qty, and Unit of Measure.  We want to add the receipt number from the RCV_SHIPMENT_HEADER table.  We cannot find it in the sources when we are setting up Supporting References.  Is it under a different name?  We tried the Shipment Number without success.

Thanks