Did you ever get an answer or know the answer by now? Same problem here.... So weird not to be able to make a return without receipt/finding order.
ConnectPOS is a POS system that supports Refund and Exchange features.
ConnectPOS allows issuing refunds as long as the order is available in Shopify orders. Customers will need to tell the cashier about the order number/date of the order/items sold. Then cashiers will search for the orders in POS and issue a refund.
Refunds for multiple receipts are not yet supported.