Ben Nye is always a good place to start. If they don't have what you're looking for, I generally avoid cosplay sites as it's a toss up as to what quality make up you'll get. The best makeup is something you could use again and has a longish shelf life. Stick to the theatrical supply stores and websites. If you have a dance/costume/theater shop in your area, go there and ask them if they have samples of different kinds of theatrical makeup. Good luck, post pics!
Upcoming Events: Katsucon 2014, Steampunk World Fair 2014, Otakon 2014, Dragon*con 2014
Harley Quinn (Arkham Asylum) - 100%, debuted at Otakon 2013
Asuna (SAO) -15%
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Kirigiri Kyouko- 5%