Here's a site that has a list of songs that might help:
Mother and Song Wedding Songs
They are more orientated to when your son would be the groom. A favorite song of mine that might be taking a different angle is "I Hope You Dance" by Lee Ann Womack. It's more of a good advice song....words to live and love by.
If your search has you coming up empty, ask some of the local wedding or radio station DJ's. Their lives are music. Lot's of stations have email addresses and would probably be more than happy to help a local listener.