All the clav sounds in the Nord are D6.
First, make sure you understand the basic structure of the keyboard. There is a piano section with sounds from their piano library (grand and upright pianos, clav, EPs, etc.). Then there is the sample/synth section with all the non-piano types of sounds (orchestral instruments, pads, etc.). And when you combine one or more of these sounds with their effects and other front panel settings, the result is saved as a Program. So far, it sounds like you're only scanning the programs, and not the libraries of all the basic sounds that are in the board.
I don't have the Nord Piano 5, but I think this will work: hit the "Layer Init" (shift+KB split) button in the Piano section. Confirm that the Synth Sample section is turned off, and that no effects are enabled (Mod 1, Mod 2, Amp/Comp, EQ, Delay, Reverb). This will give you a blank slate to work from for the clavs. In the piano section, under Piano Select, choose Clav, and use the nearby knob to choose from the four basic clav sounds (which correspond to the actual AC, AD, BC, and BD rocker settings on a D6, which are the only 4 fundamental sounds a clav has). Use the TIMBRE button in the same section to cycle through the 7 possible EQ/filter settings that emulate 7 of the 15 total EQ/filter combinations available on an actual D6 (I think those figures are right). When you settle on the one that has the basic tone that is closest to what you're looking for, you can add the effects to taste (again, Mod 1, Mod 2, Amp/Comp, EQ, Delay, Reverb), which correspond to an actual D6 owner putting his clav through particular pedals and amps of his choosing. When it sounds the way you want, save it as a Program. You can save as many clav programs as you'd like, as long as you've got Program locations available (either unused, or filled with a sound you'd never use anyway which can be replaced). Your program can also include combining that clav sound with one or more additional sounds (up to one additional sound from the piano section, and up to two sounds from the sample synth section).
Those clav sounds you found in programs D-32, G-12, J-33, I-12 are merely some sample clav programs someone at Nord created using the process above. More than almost any other board, the Nord is not primarily about playing factory preset programs, which are basically just examples of what the board can do. One of the biggest appeals of the Nord is all the hands-on controls, designed to make it easy for you to create the sounds you need. In this case, you can create the clav sound you want using the same basic process you'd use if you had an actual D6. Since the D6 itself has so few controls on it, it doesn't take a lot of time and effort to grasp what these controls do, and the Nord gives you (most of) the same controls.
Check out the board's Numeric Pad mode. Once you're in a bank, you can get to any of that bank's 25 sounds by punching 2 buttons. You can then create banks that have the 25 sounds you use most often, 25 you need for a particular gig, etc., and then access those sounds with no scrolling.