Well, what you say is true of very few frames. This usually applies to either extremely popular mass produced bikes, when a small manufacturer makes some custom parts to tweak the bike in a way a lot of riders would really appreciate. Otherwise, a few select butique brands have this feature engineered into the frames.
You would need to do quite a bit of research, but possibly linkage plates from another model Kona could work. You could possibly replace the rear shock with one of the same eye2eye but longer stroke. Just make sure your seatstay won't hit the seat tube at full compression.
It is also not all that cheap to be investing in linkage plates, possibly new shocks, etc. You may just be better off selling the frame and buying a new one with more travel.
_MK