www.galls.com Every now and than they go on clearance- a box of 70 with a 20-30 min burn time for around 50 bucks.
Totally worth it, and not the piss poor "consumer" branded ones either, these are the police/fire/ems versions.
You can also try fleet supply stores, trucker supply stores, etc.
Just remember, they cannot be put out (in any sense of easy) and are considered an explosive of sorts. Stable, but still classified as an explosive.
If you "have" to put one out, scrape the burning end completely off on pavement/cement/etc and allow it to burn out detached from the rest of the stick. Make sure there is no more embers burning on it. Can be relit if you have a hot enough flame, or another burning flare. (still a pain in the arse to relight thou)
Snuffing it out into dirt/water does nothing short of piss it off.
Also these are heavily used in the pyrotechnic business/display fireworks business.