Did you bookmark them?

Ok, then the only other way is to use the search function. Put in the title of the thread in to the search criteria box and then search on Topics.

Then, to save you have to having to do this again, I recommend you bookmark the threads:
Below the 'Start a new discussion' grey box, there are a number of pink boxes, one of them is the 'bookmark this discussion'. then to find it again, all you have to do is click on the 'show bookmarks' link at the top of the forum page (above the sticky's).

Hope that helps!

No probs