That answer is easy - China. 80 percent of the world's wigs are Chinese origin.
It is important to understand that wig manufacturing is labor-intensive and requires a strong industrial base. India is the world's leader in human hair for wigs but lacks the infrastructure for production and technology.
India primarily manufactures hair extensions and weaves with very little wig manufacturing. Increasing labor costs means China is outsourcing some of its labor to over locations like Nigeria and Ghana. Both countries have a large wig market and produce mainly synthetic hair wigs.
Another portion of China's labor went to Cambodia because of trade friction with the U.S. and cheaper labor. However, the best wig production is Chinese and in Chinese industrial clusters. The only production that has left the mainland is low-end, cheaply made wigs and wig products.