OP - in my opinion your best bet for a quality production fork is to find a take-off fork from an early 90s MTB. Plenty of them came with 1-1/8 threaded 26in forks. Lots of Treks. Might be difficult to find one that fits such a tall headtube though. If you have the $ I would just commission a custom fork from Waltworks or some such.

Re: threaded vs. threadless debate. I have ridden both many thousands of miles, and worked on both as a professional mechanic.

The advantage of a threaded system is height adjustment. It has many disadvantages:
-Very few quills have removable faceplates for easy handlebar changes, unlike threadless stems
-Quill stems tend to be heavier than threadless stems
-Quill stems tend to seize in steerers if not serviced regularly, and can damage steerers if not fastened correctly. I have seen a lot of this working in bike shops. There is nothing that is susceptible to seizing in a threadless system
-Threaded forks can be difficult to swap between frames due to the specific requirements of the headtube and headset. Threadless forks simply need to be long enough.
-Damage to threads on a threaded fork is not uncommon and is expensive to repair. The star nut in a threadless fork is easily removable and cheap to replace.
-Bearing adjustment on a threaded headset requires specialty wrenches. A threadless headset just needs an allen key

To me the biggest one is the seizing issue. An engineering solution which removes the possibility of seizing is in my mind superior. Easily installing and uninstalling cockpit parts is a bonus.