Oh, it's JAMMA? So it's a Japanese standard, so a focus on Japanese connector manufacturers is usually helpful.
A quick look at the JST website and voilà, it's the
JST V connector. (It's 5.0mm pitch, not 5.08mm, hence it not showing up in my prior parametric search. The keying pin is spaced at 7.5mm.)
The pictures of its female plug also seem to match the photos of the JAMMA plugs.
And looking at arcade-related forums, they also have no clue what this connector is called and where to get bare connectors. And they would have figured by now if it was a common part.
Nah, most people just suck at searching (just as most people suck at researching). And those that do succeed often then hoard their knowledge so they can resell at a huge markup, rather than sharing the knowledge for others. (That is, unless they were searching for themselves, quickly found the answer, and then just ordered it.)
With that said, a reverse search for 'JAMMA "JST V"' finds numerous forum replies and sales listings supporting this identification.