I would just get a new rim and also some washers and E clips/retaining clips. Sometimes the clips and washers like to take flight :rolleyes:
http://www.sawagain.com/standard-7-spline-rim-sprocket-3-8-pitch-7-tooth/
http://www.sawagain.com/stihl-sprocket-clutch-drum-washer-and-e-clip-lot-of-6/