It appears they are shippable, without hazmat fees.
Cabella’s sells the Orion flare gun kit, which is basically the same as the old Olin kit and they offer free shipping. It includes the orange pistol launcher, 6 aerial flares, a signal mirror and a whistle. If I was shipping a kit, I’d send it UPS ground with a ORM-D label (just to be safe).
I didn’t see any State restrictions when I loaded one into my cart, but I didn’t try any restrictive States as a ship to address.
I do know that you better not have one in your boat if you fish Canadian waters, since they consider it a handgun. A friend was checked on the Canadian side of the Detroit river and they found one in his boat. He was facing an indictable offense (same as our felony), but eventually ended up without a criminal conviction. He did have to hire a lawyer and pay around $5000 in fines.