I hope to start putting some collections online which can be used straight in RetroCopy, but the current method of doing boxart isn't quite as easy as it should be which is why I've delayed it. It will be the next thing I do after the NES is finished during the week.
If you go to SMSPower they have scans, or do a google search for other sites that have it. There is another thread here which details how to get them in to RC. If you want you could help start a catalogue for when the site does host them, someone is already helping doing this but if you would like to help it might be best to start coordinating with him so the work isn't overlapped.