If you like the Ventus Blue 5 R in the fairway, I would consider just replacing it with another Ventus. We don’t stock the R in the original Ventus, bet we can order it. We stock the Ventus TR in the 5 R flex. The TR is the second generation of the Ventus that they claim is more stable than the original. We do stock the original Blue Ventus in the 6 R, which might work as well. Since your driver is a 6 R, the fairway being a 6 R cold work well too. Usually the fairway shafts are the same weight or even a little heavier than the driver shafts, but it really doesn’t matter. You should go with what you know works.
The Kuro Kage and the Tensei CK Blue 60 are good shafts. The Kuro Kage is a counter balanced option and is stiffer in the butt and mid sections, but softer in the tip section than either of the Ventus options. The Tensei CK Blue is similar in profile in the butt and mid sections but also softer in the tip section than the Ventus shafts. So, of the two if your looking for a better priced option, the Tensei would be more similar to the Ventus, but again with a softer tip section (in the 60 R flex option).