Can I download early versions of Leela chess zero?

For early versions, the lczero project's download page refers you to the lc0 releases available on GitHub. For versions from 2018, you can go the lczero repository on GitHub.

Note that while the downloads from from the former repository (lc0) provide both Windows builds and source code, the older releases from 2018 (lczero) give you only source code that you need to compile by yourself.