I'd consider doing a glass-holes style of overflow and using the bulkhead to hold the overflow box in place instead of silicone. I have done this a few times and it works nicely. All you need to do is drill the same size hole in the back of the overflow box as the tank and use an extra gasket between the box and the tank.
You will have to build your own. You can get two pieces of glass cut to make the front side and bottom that span the entire inside length of the tank. Then you silicone them in place forming an "L" against the back glass. You don't need teeth on a coast to coast as the size of the overflow will allow a thin sheet of water to skim off the top.