Go to an event like LFF and BBB. I think a lot of small trade leather workers go to these events and you will be able to talk to them, get them to size you and make a set. If you are only asking for a set made in your size (and not, for example, a specific design that they don't normally do or something difficult or unusual) then I can't imagine it should cost more than 'off the peg' as from what I have seen of these manufacturers they don't tend to make a lot in advance (what you see on the stall is what they have) and if they know they can get a guaranteed sale for it, they will make it. You are looking for the sort of leather worker who is very small scale - working from a workshop in thier house - rather than one who owns a warehouse/factory