I have started compiling a list of places where you can buy cosplay.
I haven’t bought from all these places, but most of these places are well known enough. I would still encourage you to do your own due diligence.
Strictly Cosplay Websites:
Wigs only
A place of good quality wigs. Epic cosplay really allows you to make wigs from the ground up. You can use a heat iron on them. I highly recommend it.
Other places you can buy cosplay