Getting the RHD driver’s door handle is the easy part (along with the inner door locking/release mechanism). Good luck getting the lock cylinder adapted to your other door’s lock/key. There are darn few locksmiths that can cut the keys, let alone have the pieces to modify the barrels. I could be wrong, but there aren’t too many other cars that our locks/keys fit, here in the states.
I just checked Ebay.UK, and found a few right front door handles with the lock hole. I’m not sure how much work it would be to find the corresponding barrel, etc, They would likely be able to be sourced for a US car, and put into the right side door and handle. The door handle cost was about 20 pounds each