They sell them in any nautical supply store worldwide or you could order them online but they cost a small fortune. You might want to get in touch with a supplier or store and ask if they have cancelled charts. They can't be used in real life anymore, but that doesnt matter for ShipSim.
Every chart has a unique number. On the site of the British Admiralty you can see which chart covers which area. For example, chart BA 151 is Marseille. BA stands for British Admiralty.