Have a look on ebay also in antique stoves. I see quite a few in there at times. Almost any Glenwood triangle holed crank will work although my cookstove crank doesn't work on the 116. It's the right size but has a "stop" cast onto it for the front plate of the cookstove. Being a #40, you will have the grate ends protruding through the front plate and thus most cranks will work for you. My 116 has holes that the crank must fit through that makes it a bit more difficult.
Something like this may work, just ask the seller to measure the size for you.
This link is broken, either the page no longer exists or there is some other issue like a typo.