Popular streaming websites like Streamlabs and Steam elements offer overlays for download
Most websites have free overlays, but they are very general. These free versions are ideal for streamers just starting out. As you grow your brand, you will want to get a custom overlay
Many streamers turn to freelance sites such as Fiver and Etsy to hire graphic designers to make overlays. Make sure you know what you want before you decide to buy.
If you have a little bit of graphic design skills, you can make your own overlays. Websites like Canva make it easy to make any image you want, even without a lot of graphic design software knowledge