Hey Nikki, Is it made by all-glass ? I'd look at there site, if they make what you want, best thing to do is to special order it from Petsmart. They have great prices on glass.
EDIT Is this what you have ?
Aqueon » Products » Bow Front Aquariums the 46 mid way down. If so, I'd call petsmart give them a part number, see what they would charge. If not from there, try thatpetplace.com they are in lancaster, pa, about 1 1/2 north of baltimore.
Tray262