Well....about ichigo getting zangetsu without an asauchi....didn't anyone think that this is exactly why his bankai can't be stolen? It's a thing that makes him all different from the others and this is a feature he shares with kenpachi (the other war potential). Only students at the academy are gien asauchi, but kenpachi already had his sword in shikai when he found yachiru, an back then he was no shinigami nor student.
I bet there is another, hard way of developing one's zanpakuto.