I don't think you will find one. Canopies are usually made for bigger tanks/ dispay tanks. A 40 breeder is just to short a tank for one . Unfortunately your best bet is a millwork shop or diy .
Another alternative is a glass shop and have a piece of 1/4" plate glass made to fit.. I have a few pieces here I use on some of my tanks and theres no way a cat can break that.