There are a number of places you can get patterns for Photoshop. You can find them online, in books, or in magazines.
If you’re looking for something specific, like a polka dot pattern, you can try searching for it online. There are a number of websites that offer free patterns, and many of them have a search function so you can find exactly what you’re looking for.
If you don’t mind spending money on patterns, there are also a number of books available that focus specifically on Photoshop patterns. These can be a great resource if you’re looking for a wide variety of patterns, and they often come with helpful tutorials on how to use them.
Finally, if you have a subscription to a design magazine, such as Photoshop User or HOW Magazine, each issue usually comes with a CD or DVD that includes a number of patterns (among other resources). These can be great to have on hand if you want to experiment with different looks.