DIY a hood and make it nice nice. Plexi ,which I assume you'll grab from your nearest home cheapo/lowes, will eventually bow downwards after a short while. It's also a pita to keep clean and clear. Glass will be better in the long run. Easier to keep clean, and won't bow downards on ya.
The reason you are having a hard time finding a hood for the 40B is because it's mostly used by Saltwater hobbyist (myself included with my double 40B) and run open top.
Finally, a nice wood canopy can be inexpensive depending on what wood you choose, and you have the satisfaction of building it yourself. Which is always a bonus.