did you search the InDesign Scripting forum?
Or the InDesign forum for that?
If my memory is right, this was already tackled.
Search for "Missing glyphs" perhaps.
Ah. Found this one by Peter Kahrel:
That directly leads to Pete Baumgartner's method here:
Just a hint: Read every post in this interesting thread.
My problem was completely resolved.
Thank you very much!