the title speaks for itself.
I think it might work like this:
rare scrolls are obtainable after level 150
they will give you a training quest specific to the magic
after the quest it will make you replace 1 of your magics with said lost magic
what do you guys think
I imagine the primary way will be through dark sealed chests
How it does now except you can change your first magic
hecate shard but with any mutation
I don’t want Hecate shards to be tied to rng. I don’t want them to be easy to get but you don’t have to add rng to make something more difficult to get 
Lost and Ancient magic obtainment was going to be RNG regardless, dude.
it was from the very start.
Vetex is willing to change for the sake of quality.