Go to the first post and get the handle of the OP. Look in the post and find a bunch of four or more character key words. Then do a search on that user name, using all the key words, and narrowed to the smallest date range that will catch the post.
When the search returns its listings click on the originator's entry. The beginning of the thread will come up in your browser, and it's address will be in, you guessed it, the address bar. Copy and paste the address into a convenient storage spot.
When a never tried it naysayer gets to blabbing, reply and copy/paste the address into your answer. It should light up as a link to this thread.
