Not in stock code.
The current method is to set the permissions to view.post.reply.etc to a forum and assign them to a specific group.
Then that group would have access to that forum.
Via manually adding that member to a group or by auto method using number of posts.
So you could say add a group called for example specialaccess.
Then set permissions that only specialaccess can see or use that forum, your preference.
Then either you manually add a member to that group or set it to promote the member to that group based on number of posts.
