A good source of sandpaper is your local automotive paint refinishing supply store. Most carry rolls of 36,80,100,120,150 and 180 grit sandpaper. These rolls are 3″ wide and 36 foot long. Perfect size for sanding blocks or metal t-bar sanders. 120 grit seems to work the best on balsa and carbon for shaping, then follow-up with 180 grit. Don’t sand the carbon inside your house as it will get everywhere and you don’t want small kids inhaling the dust. Using a shop vac while sanding is a good idea along with using a tack rag and blue painter’s tape like Lee suggests. Wear a face mask and googles as you don’t want the carbon dust getting into your eyes. The Norton sandpaper company has been purchased by the French St. Gorbain Company and is now called Norton-St. Gorbain. 3m Pro sandpaper is also a good brand to use. Stick with the name brands for the sandpaper as the paper backing on these brands are stronger then the cheap brands. Alum. oxide paper grades seem to work the best for non-cloging of the paper.
Mike