Nookulur gopher. I like that. I don't necessarily agree that a powder fire would be hard to put out, as it really takes very little water to keep powder from igniting. Try it someday, toss a loose pile of powder onto the ground, ignite with a fuse, and hit it with a heavy mist. The small amount of heat generated by small amounts of powder is very easily absorbed, and it takes a pretty large amount of energy to ignite loose powder.
The sprinkler is simple. Buy a head, wherever you can find it, and tap into water wherever you can do it. lead the water out to the sprinkler with freeze proof plastic tubing, and switch to either copper or galvanized for the last 10 feet or so. Get your sprinkler head with a very low temp of actuation, and with a very low tolerance, so that even a small fire will trigger it, rather than requiring a big burst of flame.