Just out of curiosity, where are you getting all of this?
most of the stuff can be found on google, quarterarcade nos stuff to buy, ebay, mamemarquees.com, but as for downloading them "
http://artwork.joymonkey.com/" not sure if they are still excepting membership if you donate, but at least i believe as a guest you will be able to view the entire catalog but with a watermark, i can get you anything off that site or see if you can't gain membership etc.. Just try not to abuse the bandwith..
I don't remember what the total artwork size was i think it was 300-500gigs something like that in just arcade art !at one point i think they were doing a service of you sending in a hard drive they would copy the archive for you.
This was all on CAG "Classic Arcade Grafix" website, it was sold and bought collectivly by members of BYOAC and the member Joymonkey uploaded the entire set !