It sounds like you are going to do everything possible to find this little ones rightful owner, and that’s so good of you! I’m not sure where you live, but you might also want to try posting in the pets and lost and found section on Craig’s List. I read in an article this morning that lots of folks are using the site as a lost and found forum with some favorable results. Might be just another tool to try and find the owners in addition to everything else you are doing.
Here’s the article in case anyone is interested in checking it out:
http://www.msnbc.msn.com/id/12131061/