The elcova store has the H2 shields as well as Trailduty. I looked at the manufacturers site and I did not see any for the H3 yet. I am sure that they are working on the H3 shields and they will be available here or at Trailduty when they are produced.
Newbie,
I searched a little for magnet sheets-
This company has color options-
http://www.magnetking.com/#regularmagnet
It says cut to anysize on the home page so you may be able to special order something to the length you would need. I don't have the capacity to try too figure that stuff out - that is a man/math thing.
The medium thickness (0.030") is like a car sign magnet- which is as thick or thicker than the shields I believe. So you can get nerdy and use that as a reference to figure the thickness.