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HHKB would be great, except for finding matching replacement keycap sets for it. There are white and black, blank and lettered, and that's it (talking about the standard ANSI-like layout, not the JP layout, although I'd guess that similar would be available for that).
You can coerce a RealForce set to fit an HHKB, as long as you don't mind one or two legends not matching, and the profile of what ends up as the right Shift being off.