I presume what you are looking for is what in the US would be termed a buyer's agent. Someone who'll go out and find you a boat
and then act on your behalf? Not sure they really exist in Europe
As you are in the UK I'd have a chat with Mark Jarvis at Multihull
World on the South Coast ( https://www.multihullworld.com/ firstname.lastname@example.org
) A knowledgeable and nice guy. They also have a base in the South of France
No association with them. Just met Mark at an event a few years back and remain on their email
list even though I'll probably never buy another boat!