Depending on when the videos were made, it's likely some of the oldest ones are gone.
The more recent CTs that give such an error can be found on this site.
The reason is because this site has switched software many times over time, and only during the latest switch, content got ported over.
In general, CTs from mid 2015 to present should be here.
CTs from earlier than that can probably be found here, but the original creator of such files will need to re-upload the missing ones (albeit, not sure whether they are still around).
You could try typing what you're looking for in the search box here, and see if any of the suggestions popping up gives you the track you're looking for.