Hi Brenda! If it is a stencil you saw in a project, ask your question on the post. If you are looking for stencils in general, I buy mine online, craft stores, and even Walmart and the Dollar Tree.
Hobby Lobby, Michael's, or Amazon are my go to places for them.
Everywhere . . . Craft and hobby stores, some fabric stores, paint stores, home improvement centers, dollar stores, Wal-Mart, Target, and many on line retailers.
I like the convenience of shopping on Amazon.
Sometimes even dollar stores sell stencils, too.