Hello, I am needing a KDE image based on 18.04 not 21.04, but it seems impossible to find. Does someone have a link or torrent?

I don't believe they keep older versions of KDE Neon around once they move to support the next LTS version of Ubuntu, which is currently 20.04 - and there is no 21.04 based Neon since it is not an LTS. If you meant Kubuntu 18.04 and 21.04, Kubuntu 18.04 is end-of-life (was only supported for 3 years). If you need 18.04, you will have to use Ubuntu 18.04 (without KDE), which will supported for 5 years.