[parkanz2]

Does anyone know where to buy one or have instructions on how to build one?

Here's a how-to thread. Making a PDF vertical tank and 3D background - Dendroboard

I just made one. It's really easy. Any ACE hardware should be able to cut the glass while you wait and it's really cheap compared to some other places I've gotten it.

The only thing I'd pay extra special attention to is siliconing in the bottom, fixed piece of glass. Silicone doesn't always like to stick to plastic, so roughening up the aquarium trim should help. He may mention that in the guide, it's been awhile since I read through it.