With flash cards like the R4 3DS from r43ds.org you can bring back some of the good old days of gaming and play your old classic games right on your Nintendo 3DS and Nintendo 3DS systems. This shows Mayhem in Monsterland playing using FrodoDS on the Nintendo 3DS XL (video captured) using the r4 3DS card to load and play C64 games on your Nintendo 3DS system. Pretty amazing considering that you essentially have a portable c64 now in your pocket.
Sorry about the robot voice, but I've got a cold and can barely speak above a whisper right now. You can download FrodoDS from the official R4 site. The games can be found online, but I won't be able to point you in the direction of where to get them… though most of them are probably abandon ware now, so you are probably free to download them.
The emulator works on the DS, DSi and Nintendo 3DS and 3DS XL systems too.