It is not uncommon to have 2 calibres the same, I actually have 3 x .22LR at the moment.
Simple fact is you have to demonstrate a need, and yours does not appear to be strong enough in the eyes of your region.
Dedicated night vision, target, other sites, etc may all work, as others have mentioned, but I think you may have a bit of a problem in the immediate short term.
Have you spoken with BASC (other shooting organisations are available)?
Good luck!