You should be able to purchase the software etc from a Mitsubishi dealer or the company that built the machine. In most cases you will need to deal with the OEM (company that built the machine) to obtain a copy of the original code. In many cases you can not view, edit or go online with the PLC if you dont have that. Even if you are able to download the code from the PLC the odds are that documentation isnt there and without that you could spend hours/days reverse engineering the system.
There are others here from your country that work with Mitsubishi on a regular basis. I brought this back to top in hopes that one of them will see it and reply.