The best and only place is the download page of opencpn
There is a lot of changes in the grib plugin in the 3.3 beta version.
I'm not too sure we want the whole zygrib integrated in opencpn's grib plugin though. If you have an overwhelming feeling something is missing, express it in a feature request in OpenCPN::Tracker All Projects: Tasklist
and sooner or later someone might implement it.