Assuming your story is true for the moment, here is how to do this.
1. Pack up everything and move halfway around the world to the United States. Doesn't matter what state, but you need to move here. Step one is probably your biggest problem because it will involve money, time, visas, passports, etc. But maybe you can get away with it by being here just temporarily (a few months)
2. Assuming the IMEI/ESN/MEID is still clean, establish service with Sprint. You cannot be on an ASL acount (Account Spending Limit, bad credit).
3. Be a customer for 90 days and pay your bill on time.
4. Call Sprint and ask them for an international unlock (they will never unlock domestically)
5. Move back to Australia.
Number one might be able to be worked around if you could find a Sprint customer willing to take all the risk and add the phone to their line, wait the 90 days, unlock it and send it back. But you are trusting the phone to be sent back yourself.
Honestly, if your story is true, just turn the phone in to the police.