http://en.wikipedia.org/wiki/Dragon%27s_breath
Dragonbreath rounds are basically kind of an incendiary shot (pellets are made of magnesium). Wikipedia says the round isn’t made powerful enough to cycle the action in auto weapons, but for the sake of simplicity of implementation we can allow it do so.
An idea of an in-game mechanic is to make it ignite any burnable item in a cone; basically allowing your shotgun to become a kind of a short-range flamethrower.
Suggested places to find it: rare item in mansions (exotic ammo fits the theme), rare item in backs of gunstores (not sure on its legality), maybe found in police stations.
Reason to add: MORE FIRE and general awesomeness. Put these in a saiga for bonus points.
Magnesium powder: can be harvested from magnesium chunks with a hacksaw and lots of time; chunks should be rarely found at heli crashes (alloys high in magnesium are frequently used in aerospace applications).
Can be used for crafting said dragonbreath rounds, flares, flashbangs, used with oxy powder and a gun round to create dynamite (well, technically it’s ammonal, but whatevs), crafted into a firestarting kit, etc.
Reason to add: a way to create flashbangs, an alternative way to craft dynamite, an alternative incendiary source.
Fuse: an item that burns for a set amount of time, then explodes any COOKOFF-tagged item in its tile. Made from gunpowder and plastic chunks, for example.
Reason to add: really needed for the finer demolitions work. Sure, we have the radio dynamite and C4, but a low-tech version would be nice too.
Homemade rocket: made from sugar, oxidizer, cardboard and a grenade. Requires 5-6 fabrication, 3 cooking and a stick to craft. Essentially a smaller version of https://en.wikipedia.org/wiki/Qassam_rocket.
Homemade launcher: a pipe with a piece of scrap metal for sights, used for launching homemade rockets.
Reason to add: more explosives! homemade! Also, a resource-intensive but low-tech way to deal with milspec turrets.
Anarchist’s cookbook: contains recipes on improvised explosives, radio bombs and maybe some more stuff like casting brass knuckles from lead.
Reason to add: themed book on improvised explosives and the stuff from radio mod.
Terrorist or Anarchist background: costs 3-4 points, starts with some explosives, Anarchist’s cookbook, lockpick kit, some kind of a knife, 4 fabrication and 3 cooking.
Background info: You’ve been on the way to bomb the town hall to finally prove your point to the ignorant masses. (Un)fortunately, the masses appear to be even more ignorant now, and your brain appeals more to them than your ideology!
Reason to add: explosives-centered profession.