I don't know about the Keyblade Graveyard. While the idea of being used for nowadays Keybladers intrigues me, Xehanort did say they are lifeless keys devoid of power.
You can get a Keyblade by inheriting one, by forging one (for those who know how) and by awakening in you the gift to wield one (at least I think this is different than inheritance, for example Xehanort and the infamous Keyblade).
Then we have Roxas, Xion, Data-Sora. Roxas was deeply tied to Ventus, so that's that. Xion's was a scam, we'll see how it develops from there. Data-Sora just... I don't know, his heart became so powerful he was granted one?
Then there's Lea who basically underwent Hyperbolic Time Chamber to get one (because him having a Ceremony with Mickey was too easy... Nomura, why did you create the Ceremony if you're not going to use it?)