Thats because every de-act produced since about 1950 now has to be re-cut and re-proofed thanks to EU/Westminster. Just about everything that was out there is currently illegal to sell or transfer.
Problem is that there are only two proof houses to do the re-certification, both with capacity and working practices stuck in the eighteenth century, and consequently they are fully committed for months ahead.
You need to be aware of this in the UK "Please note this is classed as a realistic replica and you will have to be a member of a re-enactment group, military vehicle group or using it for film or theatre. We will need a copy of your membership or some other proof before we can send it " Otherwise they have to be bright orange.
But if a replica is classed as an airpistol it can be purchased by anyone over 18 and come in black or any other colour.