you might also call the PO yourself and ask the person that answers the phone to ask the mail carrier if remember it when the mail carrier gets in from route and to call you back or leave message bout it for you to pick up by calling back.
if it's a small enough po they should be willing to help.
easiest way to get ahold of the po direct, is to google the township name and 'post office' can often find it on chamber of commerce websites, etc.
it's a longshot, but might be worth trying