What's your price range? eBay is my first resource for wigs (remember, you want Japanese kanekalon fiber-made ones!) and you can get good quality ones between $25-30 including shipping~
Try typing in "Long Red Cosplay Wig" into eBay, that'd be your best bet.
You might want to hurry though, because standard shipping from Hong Kong (which is where most cosplay wigs are sold from) take at least 2-3 weeks to arrive, sometimes more, and it's really close to con-time! >3<