Try PPJN (Professional Pilots Job Network) There is a list on there of air taxi operators etc. You probably know the requirement of 700hrs for single pilot IFR and don't believe MCC would be an issue. I also understand that the CAA are looking at allowing SE public transport flights in IMC, at night and over water sometime in the future but like most things it's taking time. Therefore a multi rating would not be necessary and you could get by with a SE/IR (frozen ATPL) I think what I have written is pretty accurate but I am sure I will be corrected if not.