The best way to acquire the PCBs you want is to hang around message boards like Shmups to find out what people are selling. Quite a few of the members over there collect and sell PCBs.
But are you sure you really know what you're getting into, C_S? PCB gaming isn't cheap. A good Supergun will run you more than $300, and beyond that there are many other things to keep in mind, such as picture rolling due to differences in sync (Cave games scan lower than 60hz, for example). As Chibi noted, CPS2 boards are nickname "suicide boards" for a reason. Also, the boards you're looking for are quite expensive.
None of these things are insurmountable obstacles, but they shouldn't be ignored. Getting into PCB gaming isn't as simple as buying an off-the-shelf console. I've resisted getting into PCB gaming largely for these reasons.
The spirit of liberty is the spirit which is not too sure it is always right. -Learned Hand
"Jesus christ you are still THE WORST." -FirstBlood
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