I've taken a cog off a ND model D and used it on my ND Model A so I'm thinking a 50s model D cog should work. I'm sure someone who really knows what they're talking about will chime in with the straight poop. I've just assumed all the New Departure hub models are threaded the same for the cog.
Maybe who ever bought these has some to spare. 😀 https://thecabe.com/forum/threads/1-2”-pitch-nd-crazy-cogs-sprocket-spectacular-new-departure.200660/#post-1366505. Send Kevin a pm.