There are many stores on TpT with clip art for sale. You can use this link to search for them. Just make sure you read the rules and licenses associated with the clip art before using it!
Be sure not to include any art, photos, or other images in your products if you aren't sure that you have the right to use them. That includes images found on the web. If you are registered as a TpT Seller, please view the threads about copyright in our Seller's Forum. This one is specifically about clip art copyright. You can also read about our Copyright and Trademark policies for further information.