It's especially rough when you remember seeing it on the internet before and even had it yourself at one point. There are/were a bunch of music artists I discovered at both the old eMusic and the music section of old download.com, but those collections weren't archived anywhere in any meaningful way when the sites changed. It took me years to finally locate what I was after. It's just so draining to know that something used to easily and freely available and to not be able to find it no matter how hard to dig.

A lot of french dubs of cartoon /anime are now lost media. A small team of dedicated fans have been looking for the french dub of Keroro Gunso for years and despite being really famous when it aired it's nowhere to be found . A second Exemple is the cartoon network chowder which seems to have vanished from earth like it never existed.

What were they?

I usually assume that if I don’t find it in under ten minutes it doesn’t exist.

Preservation is important. Have you also tried IRC or DC++?

I still haven't had luck finding for the Wheel Squad cartoon, I want to rewatch it because I remember one scene that seemed pretty eerie to me as a youngling.

And you tried places like https://rutracker.org/forum/ many have english audio. What titles you were trying to find? And yes... backup/archive everything on a massive scale even if you don't need it right away, maybe one day you will.