Kenwood never made a matching transverter for the '940. Many years ago, they made one that was designed to operate with the TS-520, and possibly the TS-820, but the only source would be ebay; because they are quite collectible, they will be $pricey$.
You want Kenwood 6M? Look for a used TS-60. Again, pricey, but more current and more available.... maybe.
Here's a link to a description of the TV-506 (they also made a 2M version):http://www.ham.dmz.ro/transverters/kenwood/