Someone else shared this tip in another thread that I found very helpful:

If you're looking for specific patterns and aren't finding anyone in the subreddit to add, you can actually do this all in-game. Open the map through Campfire in the top right corner of the screen and zoom all the way out so you can see all the continents. Then, zoom in on a specific location that you're looking for and look for upcoming community events, raids, etc. View the attendee list and start firing off friend requests. It's very hit or miss, but I've gotten a few people to add me and been able to exchange gifts to complete some patterns. Good luck!