Whilst you can't buy one new, a second hand one built before the change is still legal.
https://www.gov.uk/government/publications/bull-bars/bull-bars
"
General requirements
It is not illegal for vehicles to be fitted with bull bars, although the department would not recommend their fitment unless it has been shown, through compliance with specified safety standards, that they do not pose an additional risk of injury to pedestrians or other vulnerable road users.
There are no plans for legislation to require bull bars that are already fitted to be removed. However, since 25 May 2007, it has been an offence for bull bars that have not been approved as compliant with those safety standards to be sold. Approved devices will carry an indelible ‘e’ mark (eg ‘e1 01 1471’)."
If you can get an original one, you would be ok (but check insurance as already said).