fivewits wigs is an in US wig store and they do have character wigs. Cosplay fu is outside the US(I think) but I've heard good things! CosplayWigsUSA also is a wig company here in the US, and they have a good amount of character wigs.
That's about all I can think of!
Next Convention: Anime Detour
Scarlet Witch- Avengers: Age of Ultron
Maggie Greene- The Walking Dead