An interesting point is if you obtained the game on something like Virtual Console on a second-hand Wii or 3DS, or if the game is a port and you want to download the original game. Because really it's the very similar except on another console so is it illegal?
The best bet is to make a ROM dump yourself, but don't distribute it to other people. That way you will never get caught for downloading ROMs because you MADE the dump.
Anyway, yeah pirate it. I have the entire snes, nes and gb* rom sets on my computer because I'm lazy to go and get ROMs I only want, and there might be interesting, new things.
as far i know nes still illegal from my hosting polish site:chomikuj all nes roms was removed by dmcaforce im think the did it for purpose be "effective" thats is the story i say about law :you can have any illegal game or movie but you cant distribute
im not worry about police chomikuj as pirate hosting site is in Cyprus and law in that country is other than in my contry so chomikuj administration can laugh and dont need care about prison about law here :https://www.riaa.com/physicalpiracy.php?content_selector=piracy_online_the_law