To start the bore for most duck calls is 5/8" which is about 1.6cm. I have no idea of that is a bit size you can get or not, if not how about a 1.5cm bit?
The reed material, check with stores that selling sewing material. Women that sew use it for patterns that they want to last. Especially the the ones that make homemade quilts or blankets.
The only thing that is left is the cork for the cork slot. Check with a mechanic ask for cork gasket material, try to find it at 3/16" or .5cm, or as close as possible.
The exhaust channel is 1/4" which converts to .6cm.
Marvin