You could try Harrods Executive Aviation at LHR, Jet Aviation are probably also worth a try as they have lots of bases and work from Europe try +41 61 325 2040 and take a look at
www.jetaviation.com .
You might also look into some of the new Fractional Ownership operators popping up as they seem to be ordering more new Corporate Rockets than anyone else. Executive Jet, Raytheon and I think Gulfstream are all players in this growing market sector. Good hunting - hope this helps.