This sounds bad but did you have your car painted at the same shop?.................
its not hard to get keys cut when they have them. and also you said that it was booked in to get an alarm installed, Did the Auto electrician or installer have your home address?.........
It happened to a mate of mine years back booked in for an alarm and the night before it gets stolen. they linked it back to an employee of the installation company.
just a few areas to look into. I know it sucks to have cars stolen so I feel for you and hope you have some luck tracking down the low life scum who think its OK to steal some ones pride and joy.