I have the extra set of shocks from a 2016 Z8 that I would sell. I dont know that they are what your looking for but if you were talking about the front shock measurement in your post above then they are ~2" longer. Let me know.
Thanks for the offer but your fronts are 2" longer than my rear shocks which are 17 3/8 and with my 2" lift they won't work, they would have been a perfect alternative to doing the 2" lift. If you are willing to sell only the fronts you might PM Strykerlover, he has the same DNM shocks that I do and is not happy with them being so stiff and is looking for more ground clearance as well. It looks as if your fronts would give any Z6 a 2" lift in the rear without all of the modifications to make the RZR brackets work, raising the front of the Z6 with brackets is the easy part there is plenty of room for the mod.