They're out there, and usually free/cheap.
Thats where your wrong Monmotha. I have measured and I'm looking around now. They aren't free/cheap or easy to find.
I can find 19" CRT computer monitors all day long. I'm having a difficult time finding a 19" Arcade monitor that accepts a VGA signal.
Well, they must have all been trashed, then. A couple years ago, people couldn't give the darned things away. I remember seeing postings for free 19 and 20" CRTs all over the place. The 20s were the rarer beast, though a lot of things advertised as 19" seemed to actually be close to that viewable. The real determining factor is the tube type (Mnnxxxxx where nn is a measurement in cm), but that's hard to determine without tearing the back off. The bezels often hide a fair bit of imageable area, though, so you may be looking at something that seems wrong but is actually the right size.
Any reason you HAVE to have the extra inch? Some sort of fixed mounting system that you can't replace? Most cabinets can be reasonably modified to take anything close. I've got a 29/27 crammed into my MK2 which was designed for a 25.
As for that WG on Happ's website, they aren't claiming that they have that monitor, just the accessories. I've heard from several sources that the only CRT based monitor WG still is making in any capacity is their D9xxx (whichever one is current), and those will be 29/27".
Really, 19" arcade monitors that did VGA were somewhat rare beasts to begin with. Most games that ran/run VGA were in larger dedicated type cabinets with bigger monitors. Some slot/gambling games used them briefly, but they all went LCD pretty quickly.