I've thought of calling Taig for the hard part- make me an extended Z axis screw, about 20" long. Taig would probably charge me an arm and a leg anyway, if they could even make it.
Why don't you try an X-axis leadscrew instead? They are identical threads and ends, and far longer than the Z screw. Exactly the same thing, just longer. Only cost a few bucks as well.
I bought a spare Z-axis screw from Taig and used it to extend my Y-axis. Not tough when its a straight swap like that, ends were turned the same and everything.