You can search for archived caches by GC number but not by name.
If you know the name of the geocacher who owns the archived cache, then you can check their profile and search through the chaches they own. The archived ones will still be listed there.
Also, if you know the name of a geocacher who once found the archived cache, then you can search through their list of finds.
---> That was just the way I succeeded in my special request for "Ruediger's Loch" - I found someone who found this T5 cache in 2008.
Thanks for the reply. I hoped there may be a general way to find such archived cache next time if I know only the name.