The last release of CB 1.x can be downloaded from our forge below. We don't provide older CB 2.x releases than what's available on the downloads page.
forge.joomlapolis.com/projects/cb/files
I'm not really sure upgrading is going to be a solid option at this point. You're far too behind in releases. It's probably better at this point to start with a fresh Joomla 4 and manually move data over as needed.
If you still want to go the path of upgrading I'll see about getting some of the older CB 2.x builds to put in our files archive above.
Edit: Looks like you've already upgraded to Joomla 2.5? You should be able to install CB 2.4 then.