You can typically purchase nicotine sulfate from chemical suppliers, agricultural suppliers, or online retailers specializing in agricultural chemicals. It's commonly used as an insecticide in agriculture, so you might find it available from stores that cater to farmers or crop growers. Additionally, you can explore online platforms that specialize in selling agricultural chemicals and insecticides. Ensure to verify the credibility and reputation of the supplier before making a purchase to ensure the quality and purity of the product.