Needless to say, the reverse (shotshell in a flare gun) option is an even worse idea. Not because of the recoil, but because of the blowing all the fingers off your hand. (I gather a decent 12-gauge flare gun won't chamber shotshells without modification.) Anyway, just thought I'd mention it.
There are also .410 flares that I think hi-vel.com used to sell. I assume those would be even less impressive than 12-gauge flares, but I'm not sure what you'd fire your .410 flares out of. Most full-length guns are choked; handguns are rifled and generally have a removable choke for the .410 shells. I wouldn't try flares out of either of those unless a very wise man told me it was okay (and he had all his fingers).
The only likely launcher for the .410 flare would be the derringer. Bond Arms has some very nice-looking ones ... I bet a flare could make it out of that barrel. You could carry birdshot for snakes, flares for signalling (but see warning two posts further down!), and 45 Colt cartridges for axe-murderers. Don't know if anyone still makes .410 flares though.