Your post caused me to investigate, just for fun. I used Parts Express for some old garage speakers, but yours are much nicer. I found a website that is interesting but I have not used them. They sell an adhesive just for this purpose as well as re-foam kits for many speakers.
http://www.simplyspeakers.com/speaker-repair-adhesive-mi-3035.html
Good luck.
http://www.simplyspeakers.com/speaker-repair-adhesive-mi-3035.html
Good luck.