Have you looked at the 5 or 6 different threads on it in this forum.
Your experience with the dealer sounds a lot like electronpushersviewtopic.php?f=22&t=4067
Are you in the same state?
I'd be very reluctant to try the ECU without something firmer.
Are you a member of the Australian Electrical Vehicle Association? There is a bit of discussion on the AEVA forum too.
One member in Brisbane has just bought a wrecked i-MiEV. He is going to use all the parts to convert a Cortina, but might be willing to let you try swapping some bits for troubleshooting. I guess you are not likely to be nearby if you are 300km from a charger.
A few people are trying to pull the chargers apart and replace components but I don't know if any have succeeded.
jray3 on this forum and at least one other have succeeded with second hand chargers. Their is an imiev being parted out on ebay in the uk at the moment, though I didn't see the charger listed, and they want 1500gbp for the motor ecu, but might be worth looking into.https://www.ebay.co.uk/sch/m.html?_ssn= ... =200&rt=nc
You could also try asking Mitsubishi for a 'goodwill' warranty repair. That is what they say they are doing for us. Haven't said exactly why they approved it, but we had 2 factors in our favour - that the charger was only 2 years old, having been replaced in a recall, and that we have an extended warranty certificate from the dealer that sold it.