Oh ok, thanks!
You can find closed threads by going through your post history. Or if you know with which other threads it was posted you can just guess the thread ID and edit it in the address bar. They're sequential.
You can no longer find locked threads by looking at your post history. They are now removed from both post history and the buddy. The only ways to find them, aside your secondary method, are to search for the op, and go to his/her threads, or alternatively, simply go to "browse members", and the locked thread will be visible in your buddy on that page. For now at least.