You might try Michael Percy Audio .
I know he carries a number of hard-to-find damping sheet products, but I'm not certain about the 3M sheets. Presently, the bandwidth on his website has been exceeded, so it won't load. However, if you view a cached version of his contact page you will see an email address at the bottom.
I know he carries a number of hard-to-find damping sheet products, but I'm not certain about the 3M sheets. Presently, the bandwidth on his website has been exceeded, so it won't load. However, if you view a cached version of his contact page you will see an email address at the bottom.