I can happily do that for you Aaron if you're able to produce the code to cycle the screen colours
That would be awesome. Any of the Astrocade-based boards would work.
Like you say, that's the only way to get the values without including the monitor although you may still need it to be done using two or three different RGB encoder boards because of the somewhat obsolete and strange component on there (we're taling about the board with the paper tube, yes?).
Not sure which board it is, but it's the one that outputs RGB.
I can borrow two or three of these little PCBs if you did want to check the results from more than one since another collector in the same town has a loft full of this kind of thing.
I'll leave that up to do, since you will be doing the hard work! I think the tediousness of getting 768 values from an oscilloscope will drive you insane relatively quickly.
It will probably be a couple of weeks before I have time for it. I'll need your email address to coordinate. Either PM me or send it via the contact forms on mamedev.org or aarongiles.com.