Benster492 - Threads remain on the forums until they reach page 50 of the forum section that they are in. Once they reach the end of page 50, they are removed from the forums. At that point, there is no way to reinstate the thread as it was without reposting it entirely; there is no "archive" of old threads.
Typically, when a thread has fallen off the forums, it is still in Google's "cache" of web pages and can be found through a Google search for the thread title, and then selecting the "Cached" version to view the page from Google's cache. I was able to search the thread title and find a result for it, however, it does not appear that the thread is in Google's cache any longer, and cannot be retrieved in that way either.
I'm afraid that I am not aware of any other way to retrieve the old thread's contents for you to be able to start a new thread without having to do it from scratch.