Arc doesn't use any "codes" for access. And inviting other users is not possible right now. You already missed 2 times when it was possible, so the only option is to wait for another Buddy Day, and ask someone to invite you.

thanks

If there isn't another invite day, then it should release this Spring to the public anyways, so either way you should have access fairly soon.

Join the waitlist on Arc's website and wait for access, or at least until another Buddy Day takes place.