I don't think they pop up all that often and when they do pop up they tend to go quick. I have been after one for a while just so I can see if I can clone it. I have thrown something together myself but it uses a workaround to prevent the accessory from disconnecting. Basically I have to keep one button connected at all times to circumvent whatever it is they put in their box that I can't see.
There was a bigger version of the K..AT which is harder to find and I intend to build something closer to that. More switches, more pedal sockets and some rotary encoders for shuttling the cursor around etc....basically it's possible to assign 3 of the switches to an encoder so that you can move a cursor in the direction of rotation (left and right or up and down) and then press the encoder to enter or remove data.