I really like girls with unnatural hair colors like bright red and pink. Where do I find them? What dating site do I go to?

If there are none of these girls in your school/workplace, then my suggestion would be to visit the two places they are most likely to be:

• Alternative clothing stores in your local area (especially ones that sell bright colored hair-dye like a line called Manic Panic).
• Shows of bands that these kind of girls might be into.