Yesterday I spent about an hour at a couple of wrecking yards.
I had to go through a few doors, but I ended up with a good supply of diaphragms that are in good condition.
One constant that I noticed is that the diaphragms closest to the hose connection fail first. I have decided to go ahead and check all of my diaphragms this weekend and clean & condition the rubber. I believe this may extend the life even more.

Thanks for the help !
Robert