Unfortunately they don't stock heavy loads. They stock one type of 180gr but at an astonishing £52 a box. Other than that their heaviest is 165gr. These rounds are for a double rifle that need heavy loads for the barrel twist
Who have you tried? Sussex Guns near Battle might be able to help you, as Might Chris Potter in Tunbridge Wells, or Diamond Guns in Heathfield. The couple of times I went to Andersons they were rude and unhelpful (and VERY expensive) so I couldn't recommend them anyway.
Chris Potter always tried to help me, and despite being known for not being cheap, actually they will compete on price. You can at least have the conversation.