What I would do is order a pair of keys from a local Mits dealer, remove one of my door lock barrels, take the lock and keys to a locksmith and have him (or her, I know a lesbian locksmith would you believe ) code the keys to the lock. I'm from Melb so I can't recommend you any good dealers in 'Brisvegas', shouldn't be hard to find one nearby through Google mate. If you're not confident in removing a lock yourself, you could have it towed to a dealer and have them do it (I assume they can cut/code keys..) you'll be paying for it then though.
I'd take the cars' rego papers to your local mutsi dealer, along with your id, tell them that you've lost your keys and need to get the key code (they shouldn't charge you for the code). Then buy some blank mitsy keys from the same dealer, take the blank keys and the code to a locksmith who can cut keys to code (not all locksmiths can), and they'll cut them for you. Will cost about $20-$25 for each key cutting, as cutting from code is more expensive. I've had to do this before, worked for me.