I Googled "Miterite Holiday Designs" and in a post on 3-21-11 by "Jan in VA" she wrote the following. Maybe you could contact her for some help.
If it is 8" wide, it was probably the Miterite ruler from Holiday Designs; mine has the date 1984 on it! Loved that ruler when I first started quilting; wonder why I got away from using it? Gotta but it back on the ruler caddy.