Hi Geoff,  You can get fish glue from Columbia Leathers in
Columbia, Pennsylvania.  Great folks, great service and great products.
I visited them last year and they were most cordial.  Showed me around
the place, introduced me to their employees and showed me how they
handle leather.  They also advised me on a couple of technical issues.
Although I need leather only occasionally, I can call them and the
goods are sometimes at my home the next day.

By the way, the fish glue is very tacky and fast drying.  They also
have a really good flexible glue for gluing leather and felt.

Their telephone number is 800-423-7003.  Leave a message and Darlene
will call you back as soon as possible.

Regards
Craig Smith
near Rochester NY  USA