I have the same issue with the 1026R that I have and based on what I was told by my dealer working directly with JD brass, they not only have no diverter valve option, but also have discontinued the 3rd scv option.
My 1026R has the independent lift as well and I wanted a diverter so I could mow with the loader on to help move things out of the way as needed. It doesn't bother me as I don't get close to the house or anything with it. Just trailers, and other things like pallet stacks of materials, etc. Lumber, etc which I do move occasionally. I will eventually get the JD QA forks and mow with them on likely.
Anyway, back to the lift. I have thought about how to do this and I am not convinced the best setup on these independent lifts is a hydraulic one. Looking at the size of the cylinder and the force needed to raise and lower the deck, I think swapping that over to an electric cylinder would be more functional and would be a drop in fit. I have some measuring to do and source some parts, but in order to make my 1026R fully functional without the hydraulic connector swap, this may be an easy project to do. I worked with Electric cylinder actuators years ago and they take little power, have lots of force on some models and fit in small areas depending on the extension length needed. They also provide force both directions. It could easily be connected to button similar to the turn signal indicator on the dash for raising and lowering the deck arms. The punchout below the steering column for the additional buttons would be perfect for that switch location.
For so many things to be quick detach on these, I think that was a poor design job for JD to not have another connection point for the Independant lift.
