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The world needs more good emulators, such as XMESS and MAME. But where do you get the ROMs from? Check out the internet archive with a good broadband connection!
Try the following links: https://archive.org/details/MAME_0.151_ROMs and https://archive.org/details/MESS_0.151_Software_List_ROMs for some ROMs.
There are probably more, if you look at the "software" section and if you also try the "search"