It's not an IDE interface, it's a simple as it gets. The ribbon cables connect the key matrix circuit board's switch actuated connection as they'r made to a controller on the motherboard.
Unit much like the Portable NumPad
4x4 jeyswitch matrix
Controller output to LCD display
You'd want a controller that outputs USB, such should be available off the shelf.
If you have a KBD you don't care about or can get your hands on a dirt cheap PS/2 KBD, tear it down and examine the membrane switch matrix/controller setup to get an idea of what's going on in there.