Are you looking for a company which offers a build service (you choose frame and electronics) or do you look for company which will cut your drone design out of carbon fiber sheets?
@Koti many drone shops offer build service. I know drone-fpv-racer does offer it. It's a shop based in France. They recently had a fire but seem to be in business again.
I m not sure but I think Rotorama in Czech republic does it too.