Official IC2 Classic Github Page. IC2Classic Bugtracker
If you want to access the IC2Classic Beta. Here you can get it.
Not bound to the beta.
If you want to use IC2 Classic in your Modpack, i have nothing against that and permissions are given as long you do not break the IC2 Permissions.
IC2 Permission: http://forum.industrial-craft.net/index.php?page=Thread&threadID=344