There is arda wigs, which has rather high quality, most wigs come in most colors (you can refer to their wig color page to choose what you'd like) - arda-wigs.com/pages/medium
There is epic cosplay wigs, another good quality website, same story as arda, you can choose wigs by color - www.epiccosplay.com/pink-en/co…
And then there are wigs on ebay, which can be a hit or miss on quality. Sometimes you find fantastic wigs for very cheap prices, and sometimes they're not as great. You'll want to pay attention to seller reviews, and how much information the seller has on the wig. (fiber, quality, etc. You can generally tell from the description if they have experience will selling wigs or not.)
a few different ones to get you started.