Contact the nearest railroad yard - to ask where they get theirs, not to get theirs . . .
I grew up near the GTW (Grand Trunk Western) railroad yards in Chicago, and as kids we would scavenge partially-spent flares that the railroad guys would use for signaling . . . IIRC, they were handheld and I don't recall ever finding the stub of anything more than a 5, possibly 10 minute flare. After signalling, the guy would throw the flare in the air - contact with the ground would extinguish it. And we kids would roam the tracks to salvage the unburnt "flare juice" for our own amusement.
The railroad flares never had the "spike" at the bottom, just a cardboard tube extension for handheld use.
On the 4th of July, many folks would burn flares in front of their homes; I remember even the Walgreens drug stores would carry them in various colors, but I don't remember
ever seeing one more than 30 minutes.
