Not pleasant ones, but try to source a set of locks and an ignition barrel, then cut off the ignition barrel and fit the new one. I don't envy you though, as that won't be fun.
I had a similar problem with an old Ford Capri, when my dad snapped the key in the lock. I fitted remote central locking, cut off the ignition barrel, re-routed the ignition wiring, wired in a hidden switch, a hidden push start and had an immobiliser with a fob, that HAD to be in the car for it to start fitted. No one ever stole it. But to be fair, I don't think anyone ever tried.