No one knew what I was talking about at Radio Shack or the hardware store, so I ordered one. I guess I'll find out in a few days.
If the internal shadow mask is dislodged, what do you suppose my options are? Would it be a complete loss? I was really excited to have a VGA ready functioning triple-scan monitor. 
New (to you) tube. They're pretty easy to come by, depending on the monitor in question. (Some tubes are rarer.) If you're very lucky there may be some old wizard who still runs a TV repair shop nearby, who has tube re-phosphor gear. Apparently they're around but I've never even heard of one near me, and I'm near two very large cities.
Such folks can actually disassemble a tube by taking the front glass off, cleaning the old phosphor application off, applying a new phosphor coating, fixing/replacing the shadow screen, putting it all back together, drawing a perfect vacuum again, and getting it working again. Basically a full tube reman. It would very likely be cheaper to simply replace the tube, but if you had a very rare tube with burn-in, this is how you'd fix the burn-in without replacing the tube.
Before anyone challenges me, I read about those folks on this board a few days ago. Apparently they exist, but no one seems to know who any of them are. Maybe they don't exist anymore.