Installing a door next to the driver in a 345 would be an incredibly difficult if not impossible task. For starters the front cockpit framework is fabricated as a unit. There are two cross braces running parallel to the floor in the area where the seat pad sits to help protect the driver in a side collision.
I would think removing those two braces would be a serious detriment to driver safety.
Another aspect would be how to deal with the cockpit window. You would have to come up with a complete rework of that window to cut it into two sections. I'm not even sure how a person could do that.
About the only sane option for a door on the drivers side would be to install a normal entry door right behind the driver. That would be a relatively straight forward task that would probably be doable.
I find it interesting that a drivers side cockpit door is required but not a passenger side cockpit door. Apparently whatever country you're thinking about importing the coach to doesn't care about the passengers.
If you're serious about installing a door and one behind the driver is acceptable I have a door and frame assembly from a 345 that would likely work.
Good luck in whichever path you decide to take!