The NFPA has a specific standard covering the instalation and maintenance of sprinkler systems.
Anything used with a sprinkler system must be rated for the use; that is, specifically tested and listed by UL, FM, etc. While the parts may look like ordinary plumbing pieces, they certainly cost more, and usually have the mark of the testing agency cast or stamped onto them.
In general, (there are some specialty applications) all sprinkler heads must pass the exact same tests- therefore, it is not critical that you stick with the same brand of head.
Places like Grainger, McMaster-Carr, and others sell repair kits that typically contain six heads and a wrench. Every floor or building is usually required to have one but I know prisons are different).
Rather than drain the entire system, there are carbon dioxide powered, or refrigerated, devices that are made to go on to a pipe and freeze a short section. This "plug" then allows you to work on one section, without draining the entire system.
To facilitate repair, you may replace the head while the water is flowing with a short nipple that has a valve on it; once in place, close the valve. Freeze the pipe upstream, replace the head, then let the plug melt. No need to drain everything.
