There are some cracks/fixes/patches out there for the Classic NES series (and the later entries in the Japanese series as well). I neither have a link nor do I know if those may be linked on GBAtemp and never tested them myself.
If those cracks are just patches that replace small parts of the ROM without containing the actual game, then linking should be okay. (The problem with linking cracks for e.g. Windows games is that they are often prepatched .exe files that are the complete game which obviously means copyright infringement. I guess this is why the forum rules just state "No cracks!")
It is worth noting that mGBA emulates those games correctly without any patches. On the new 2|3DS series the emulator is worth a try.