The first thing to establish, and you cant see from your photo, are the plastic studs on the arch trim that the clip pushes onto still there or have they broken off?
Its more likely the stud has broken off as the clips are normally firm.
If so you need a arch trim as well as clips?
Try RealOEM or bmwminiparts for the prices/number of the parts you need etc
Ps the car looks a bit mucky