Hey there! You won't find a lot of hair extensions in the Oberlo Marketplace. This is because the sale of hair extensions is prohibited when merchants are using Shopify Payments as their payment gateway. It's a high return item and there have been many instances of inauthentic products being sold so the policy was changed to not support the sale of these products.
When searching for suppliers, it's best to simply search for the product and determine based on those results which supplier has the best offering. I hope this helps! If you have any more questions, please let us know.