What's your plugin version? I can see the filter in that menu on my mac.
All good with that version here:
Maybe something is wrong with your installation? The toon shader appears fine, right?
yes, no problem with the toon shader appears at all. I installed twice in last week but nothing helped with the problem. it's so confusing.
What happens if you try to add the Contour filter from the toon shader UI? Is there anything in the log (console)?
I wonder what happens if you remove or rename the plugins/C4DtoA/c4dtoa.mtd file.
Also it would be interesting to see if the filter is listed when you run kick from the command line (C4D_DIR is your Cinema 4D folder):
C4D_DIR/arnold/bin/kick -nodes n