If you haven’t used a referral link yet you can retroactively do so to get 1 mil unallocated SPs.
You can choose one from the below thread that is officially placed so people can put their links there (but nowhere else) on the forums or choose one from elsewhere (unfortunately even in-game people spam their links all the time).
Best if you can find one belonging to someone who offers other good benefits alongside what the link already provides to get more out of it than just the 1 mil SP, they will get rewards if you go omega so make them pay for the benefit instead of just supporting someone who spams their link without giving any additional benefits. 