There are many places that you can go to in order to get Hair Chalk products. When you're looking for where to get hair chalk, a few places to look are:
1) Online - Pros: Large selection and user reviews to go with them. Cons: Shipping Time (unless you have Amazon Prime or Shoprunner or another 1 or 2 day shipping service). You can try Hair Chalk On Amazon
2) Local Art Store - You can buy Soft Pastels at a local art store (like AC Moore or Michaels). Pros: Same Day, No Shipping. Cons: May not be the quality you want.
3) As Seen On TV - Hair Chalk is getting more popular so you'll probably see some ads on TV for it that you can order from.
Here are some Products you can try: