I am the owner of a private equine based game site that was designed for educational purposes, however I am always getting spam registrations even though I have the verification stuff in my registration settings. There was an invite package created however it was for the 1.1.0 smf forum and there has been no updates for an upto date version.
My request is for an invitation by admin mod that will allow registration to the forum only if the member has been sent an invitational code by the administrator.
You can already obtain something like that: disable registrations, create users from the admin panel and send them the password.
If you don't need other members to send invitational codes that could be an option.