I have had the fortune of being able to obtain bladders from several local sporting goods outlets over the years. This however, appears to be changing. This afternoon I stopped by my local Big 5 store looking to buy a bladder, which I have been able to do in the past (they carried the Everlast line). After thoroughly searching the fitness area and not finding them where they have been in the past I asked the clerk, who took me to the store manager.
He informed me that the corporate management had decided to no longer carry them, as they were only $5.00 dollars cheaper than the Everlast Vinyl bags, the rational being instead of replacing the bladder, just buy a new bag. I explained to him that what I had was "old school" stuff, built to last, and that I wasn't interested in purchasing the new bags. He sympathized with me saying that it was out of his hands, he couldn't even special order them.
There is one local independent sporting goods supplier in the area that has carried the full complement of bladders. When I'm in that neighborhood I'll stop and see if they still do. If not, then I guess I'll have to order them online and start keeping a couple spares on hand.