I used to have all of that stuff available online. Don't know if it's there anymore though.
Getting a working FBL, CoinOPS (MAME) and ScummVMX set was some of the toughest work that I'd accomplished while working on the Box. Thankfully, since I came so late, there has been very few updates so the sets were relevant for much longer than when the original XBox scene was in full force.
I haven't stayed in the loop for a while, so there may have been some minor updates to the sets, but even if there were, I would recommend Googling the "RessurectionXtras" "FBL" "CoinOPS" and "Scummvmx" sets. That way, when you have all of those, and using romcenter, you will be able to tell what you're still missing for the updates and rather than downloading full packs from scratch that may not work with the updated cores you will only have to find the missing parts.
If you can't find them because they're no longer available (which may be the case)....
I'm sure with a little research here you can find somebody to ask about where to find them.