You need to look into 3M Crystalline. So clear you can put it on the whole windshield. Amazing stuff. Uses nano-technology. This film rejects 99.9 percent of UV rays (with a total SPF rating that exceeds 1,700), 97 percent of infrared radiation, blocks heat, and is nearly completely invisible to the naked eye.
Will that work?? 
No, I just want a strip, perhaps 4" wide, that goes across the top of the windshield. The top edge of it would be about a 60% tint, fading out to 0% tint at the bottom edge.
Come to think of it, is the tinting of the shade band in a standard windshield, in one of the two layers of glass? Or is it in the plastic sheet between them? Because if it's in the plastic sheet, maybe I could get my hands on one of them and cut off the top part for a shade band.
Ah, here's the answer:
http://mainland.cctt.org/istf2007/manufacturing.aspSo even if I could get a layer of this PVB stuff, it would not be shaped for my windshield. So much for that idea. Maybe that's why nobody sells them., with the correct shape to fit the windshield?
Using the word "eyebrow" in an Internet search works better than "sunshade band". I found someone did this with a band that has a gradient of solid black with "holes" transitioning into dots. Accomplishes the same thing. Done by Ziebart, apparently.
Then there's digital vinyl printing, better known for "wrapping" vehicles in advertising. One would think they'd have the technolgy to do a gradient eyebrow.