The problem, as described, is that BP shooting is a niche market. In fact, we love it because it is. We love that it connects us to generations of other shooters long before us. We love that it allows us to do things the old way. We think there's a certain beauty in the lines of a wooden stock...the elegance of a lock...the intricate details that show that someone thought enough of the sport to invest hundreds of hours to make a single gun. We love the smell...the sound...the smoke. We embrace the challenge of mastering that which our forebearers discarded for modern efficiency (which has it's own beauty that many of us also appreciate). We are not the norm. We are the crazy sort who take pleasure in doing things the hard way. Even if we were living in the times we act like we're in, we would be those people who embrace even older weapons, because that's just who we are.
The interesting thing is that though we will never be the norm, we take part in a unique hobby - shooting BP is one of the few obscure hobbies that actually attacts the norm. I've found this to be true time and again. I got into this hobby doing pirate festivals, and I'm part of a crew that contracts out to do them. Our crew makes the shows exist. We fire guns, and the "normal" people flock to us from miles around. They have no choice - there's just something instinctually alluring about it. If you spend a second to look at the "do you share your rifle thread" you'll have more evidence of this. Normal people...even those that don't like modern guns...love blackpowder.
That said, I think there will always be interest in blackpowder. It's a significant part of our heritage, and it has a natural attraction. Of course, not everyone will jump into the hobby just because they appreciate it. It is a very time consuming hobby, and most normal people wouldn't be willing to sacrifice their other interests to get into it...but some would. It's up to us to expose them to it, and teach them it's ways.
Oddly enough, we get help from all sorts of sources - movies about pirates (i.e. Pirates of the Carribean) and wars (i.e. The Patriot), tv shows which are set in the time periods (i.e. John Adams) or simply try to analyze old weaponry or "myths" (i.e. Mythbusters), books which romanticize or describe the periods, modern gun lovers, historians, etc. We may look at some of these sources and, in our arrogance, scoff at them as not being HC/PC/or just not to our standards. We must never do that. While we may aspire to be more true to the hobby, they are all things that serve it. If a remark must be made, have the presence of mind to make it out of earshot of those that wouldn't understand.
With regards to availability, it is unfortunate there are few US suppliers of BP guns. There are a number of artillery suppliers, but in fact, I can only think of T/C as an American manufacturer of traditional firearms. Even when CVA stopped dealing with traditional BP, they, like Traditions and Lyman, were selling imported traditional guns. There are other suppliers, like Pedersoli and the Indian manufacturers, which continue to produce functional tradition BP firearms. While some people would say that the shortage of American manufacturers is a bad sign (and I'd agree), it is not something unique to our hobby, and in no way indicates the pending collapse of it.
I didn't grow up around guns. My total experience with them was shooting a .22 rifle when I was in the Boy Scouts. My interest in modern guns is only due to my interest in blackpowder (though I continue to prefer BP over modern). I got into this hobby about 5-6 years ago, and my first gun of any type was a Pedersoli Kentucky pistol. I've since accumulated 3 rifles, 4 additional pistols, a Japanese matchlock, and a cannon. I've had no issues finding these, and many of them were purchased used, some for less than $50. It is definitely an accessible hobby to anyone who wants to get involved, and the guns are available if you spend a little time looking (if you can't find a deal on a gun, I'll sell you one of mine at the exact amount it cost me).
I'm 30, and not one of the people on my crew is over 40, and we regularly have people shooting with us (many that we taught to shoot, and that are shooting our guns) that are still in their teens, so you don't have to be an old timer to appreciate something that's old (nothing against old timers - I plan on being one some day, and I expect I'll still love blackpowder)!
Sorry if this is a bit long. After reading some of the negativity I felt I needed to say my piece.