First, check the libraries... there are gazillions of maps online at microstock agencies, excellent quality down to just silhouettes.
Second, I have maps in my port, they still sell, but are definitely not the biggest-selling niche in my port due to the competition.. I had to prove to the agencies that each map was drawn from a public domain source, or they reject them for Intellectual Property. Be sure your maps are traced from public domain maps, because the agencies are pretty sure you are not the original cartographer.
Did you mean to say "free to download," are you wishing to give these maps away to the artists here, or do you wish to upload them to microstock agencies to sell?
Good luck.