If you have a local fly shop, ask about patterns they need in their bins. Learn to tie them well. If they like your work, you have a ready market. You could sell them that way. Selling on Etsy or online is much more challenging.
On FlyFlasher.com you can find 34,312 flies from all over the world. Flash your own fly patterns, upload your current work or search for inspiration. The flies are tagged, so you easily can search for them.