That's slightly ambiguous. Is your definition of a "modern space cadet" keyboard that it has more modifier types? Or that it has more keys? (Bear in mind that one could go back to a 101-key U.S. PC/AT keyboard and still have more keys than the 100-key space cadet keyboard.)
For keyboards with more keys (and yet no vendor-defined private HID usages), one can look at the keyboards available in Brazil. Some of the "multimidia" keyboards from the likes of Multilaser, C3 Tech, and Leadership have the 107-key Windows ABNT2 physical layout, with anywhere up to 20 further multimedia keys.
But these keyboards don't have keys engraved with more modifier types beyond the usual five.
I am referring to a keyboard with a multitude of extra keys. The layout doesn't have to be exactly like the original space cadet keyboard of course, but having some 50 extra keys surrounding the normal qwerty portion, as well as some 10 modifier keys is basically what I'm looking for.
For keyboards with more keys (and yet no vendor-defined private HID usages), one can look at the keyboards available in Brazil. Some of the "multimidia" keyboards from the likes of Multilaser, C3 Tech, and Leadership have the 107-key Windows ABNT2 physical layout, with anywhere up to 20 further multimedia keys.
But these keyboards don't have keys engraved with more modifier types beyond the usual five.