Namco released a collection that includes 2 official demakes for the NES: Pac-man CE and Gaplus.
The roms have been extracted and shared out on the internet. I can't tell you where to find it, but you can do google search and should be able to locate them. Both are playable on original hardware if you have a flashcart.
I can say Pac-man CE runs and plays really great on an original NES. I'm going to try out Gaplus later tonight, but I've seen some streams of it today and it looks like it's a great version of Galaga 3.