I think you are doing the right and responsible thing in exhausting every avenue you can Zen, to ensure an owner isn't out there somewhere who loves him, too.
I also agree that many elderly ppl don't get their dog to the vets for micr-chipping and such. They are in a different time-warp, so to speak. And this dog is certainly a breed that I could see owned by an elderly person.
I hope for your sake no-one is found as you really do appear to have taken to him, and you also sound like a caring, wonderful person who will fill this little fellow's life with love and joy.
All the best. I'm really sorry if it comes across to you or anyone that I am 'raining on your parade', but I just don't want you to feel that sort of pain later down the track.
All the best.