To update you, I found dried yellow croaker bladder in a market in china town, but have yet to try it out.  I also found bona fide sturgeon bladder glue from a bow maker in France. He sold me 100 grams of dried and cleaned bladder for a little less than 60 euro, shipping included.  Pricy since the hide glue I use is 8 bucks for the same 100 grams.  It works well though, as per my experiments, and I get an open time exceeding an hour at 12.5% mix ratio to regular hide glue.  My measurements are approximate.   Once I experiment with the croaker bladder, I will report back.  Thanks for the help.