It's not a good idea to use any item without permission.
You should either commission an artist to create work for you from scratch, or if you want to start from clipart, you should look to a royalty free clipart website and make sure you check their terms for use of their graphics on merchandise for sale.
You should either commission an artist to create work for you from scratch, or if you want to start from clipart, you should look to a royalty free clipart website and make sure you check their terms for use of their graphics on merchandise for sale.