I don't know how many, but I do have some speculation on why. Red heads were always the lesser in English society. So, a sign of poverty or lower class would be to give them red hair. It doesn't help that various artists were of that lower class anyway. Thor is traditionally red haired to match with the working class, but he was changed to blonde in comics and shows.

Decades later and redheads are seen as equals. So, the people creating things need to prove the character is lower class. The best answer is make them black.