APP is alive and well, and seems to be the propellant of choice for a lot of shooters in the smokey categories. I use it sometimes but prefer real BP. It bugs me (just slightly) when people say they shoot BP but they are shooting subs. They are shooting in BP Category, yes, but not BP.

Almost no gun shops, or big box stores, sell APP. You have to order it, and I'm not sure if you can order less than a case. Cases are 12 lbs I believe. Shooter's World Multi-Black is same thing, made by APP. Natchez has been carrying it recently, sold by the pound (though currently out of stock). So last time I ordered primers from them ($ouch$) I added some smokeless powder and 5 lbs of Multi-Black to spread out the hazmat and shipping costs.
added: I think the APP guy pretty much always has it in stock.
also added: if you get it, get 3F as 2F is rather chunky and doesn't meter well through powder measures. Also, used to be APP was really dusty, but I hear the newer stuff is much better.