I've you've downloaded anything from the archive using one of the downloader tools, you can search for "*_meta.xml" on your storage drives. Those XML files will either have <identifier-access> with a full URL or <identifier> with just the slug you can append to http://archive.org/details/<identifier>.
If you have anything downloaded that's now missing from the archive and don't mind sharing that info, please reply with the URL or identifier. I''ll publish a complete list. Boost/repost if you want to help cast a wider net.