We are not wigmakers so we do not buy hair. The following are sources I know of in the US that may be of help.
The Hair Trader is a website where you can go and list your hair for sale. This is the best website of its kind that I have seen. It is a simple and straightforward way to show the hair you want to sell to prospective buyers, and the listings are free. You can go to thehairtrader.com or contact Jacalyn at email@example.com.
Cindycut.com offers to buy hair if their criteria is met. You can find them at http://www.cindycut.com/buyhair.htm.
Here is another link: http://www.europeanhumanhair.com/
There is also a website called World of Wigs, which I have personally contacted and was told that they purchase hair for use in repairing wigs and hairpieces. You can reach them at firstname.lastname@example.org for more information.
There are some caring people in Ohio who take donations of hair. Your hair could make a world of difference to a needy child. Wigs for Kids is a non-profit organization that accepts donations of hair to make hairpieces and wigs for children suffering from hair loss as a result of cancer treatments or Alopecia Areata. Presently, hair pieces
are often considered "cosmetic" and not covered by medical insurance. You can access their website at www.wigsforkids.org.