Part of the problem is the distributors don't care because they have no skin in the game. Our local lost almost $45k in kegs in one year because the distributor did not track them down, or perhaps better said, did not track them at all. For a small brewery that is a kiss of death and they are lucky they got by.
Good on you for trying to return the kegs. If it were me I'd go to my local bottle shop who sells kegged beer and ask if I could leave them with him. They generally will be in contact with all the major distributors.