There is no "current" version of cocoaDialog. The new version is still under very slow development, but there's nothing released yet, and probably won't be for a while.
The last actual working release was the 3.0 beta 7 version from about 5+ years ago now, which the cD developer now refers to as the 2.3 version I think. The new one being worked on is being called "3.0"
You can try using that last beta release, but don't expect it to work very well under current macOS versions. It started having issues with macOS around 10.11/10.12 and hasn't gotten better since then. It still mostly works however, so if you don't mind working around some issues and odd error output because of outdated code, you could still use it for basic dialog messaging. I would probably avoid trying to use it's advanced windowing styles like the progress bar, checkboxes, etc. at this point though.
Unfortunately, I can't really help you with how to find it online, since I think the original download links no longer work. It's not easy to find that version anymore from what I recall.