I noticed an ad in QST for the new Begali key for the KX3, KX1 and FT-817. It mounts to the radio, but doesn't plug in like the Elecraft built in keys do, you have to use the normal CW key input. It is fine piece of equipment.
The link to the Begali website is http://i2rtf.com/html/adventure.html
I have no commercial interest in the Begali, but I thought it worthy of mention. It is a little pricey, but such is life.