See another related thread on this forum which is discussing fuel tank issues
I'm not sure if the diesel tank is the same, maybe start a new thread as you'll have more of a chance of an answer.
I'm wondering if it's possible to actually repair your tank. I know it's possible to re-line a petrol tank. As for the shield. Can it not be cleaned up and a metal patch welded where the hole is? Ask the mechanic and do some research.
As for used, there's a Lexus breakers in Accrington. I know they have quite a few Lexus cars, I've actually been there in person for a couple of trim pieces. Look them up as they do post items.