It depends where you are. I'm currently in Florida where there's a huge firework show on the beach down the road so people tend not to light their own and just donate towards the huge firework show. In my hometown in Texas, there's a load to like 2 in the morning because there's no firework show.
And no, they're probably the easiest thing in the world to obtain. There's literally a shop in every little district where there are deals with like "10 Fireworks for 10$"