Former Postal employee here:
Try contacting the "Nixie" section(s) at GMF's (General Mail Facilities or "main post offices") between mailing point and destination point. Mail that has been damaged to the degree they can not determine destination address or original mailing address is forwarded to the "Nixie" section -- if they have no idea where to send it or to whom it should be returned. Sometimes the outer packaging is destroyed or the contents are separated from the original packaging... and the Nixie section is responsible for undeliverable mail and/ or contents. (loose money, bonds, merchandise...) They are required to hold such items for a certain amount of time (I think it's like 6 months.) You might get lucky... they will return these items if they have them -- postage due, of course.