It seems likely that some vendors might stock that part too...
Just to mention; The proper key will be sized in metric, and must fit in the keyway and sprocket snugly. No glue or other goop is needed.
With patience, you can file a larger key to fit. Any play must be avoided as it will lead to damage of the keyways, or shearing of the key.
As I learned on this site, "pinging" of the key could be necessary to assure that it will stay in place.
Let us know what you figure out.