Fanfiction.net is also a good place to look. There are many writers who create stories based on different fandoms. However, the quality can vary. Browse through the Avatar: The Last Airbender section and search for Sokka x Ty Lee specifically. You might need to sift through a few pages to find the ones that interest you.
Another option is Tumblr. Some users post links to their fanfictions or reblog them. You can search for the 'Sokka x Ty Lee' tag on Tumblr. Additionally, there are Tumblr communities dedicated to Avatar fanfiction where you may find some great Sokka x Ty Lee stories shared by fans.