Been dealing with Silverwings since 2003 and have never seen what you are looking for.
Hmmm.....
Thinking about how one might create such a thing.
Rear mount points for a flat roof shouldn't be to hard to figure out.
But even with angled supporting arms going forward to support the roof,
The wind at highway speeds would overcome it like driving with a convertible top half way up.
Front mount points no matter where you go, there is plastic in the way.
You would have to find frame points that you could drill through plastic to...
Even if you reinforced a windshield and had clear plastic that could snap to it and go back...
I think that would still put a lot of pressure on the windshield.
The picture below is a Silverwing Trike with Fehling protection rails.
In theory you might be able to attach a flat top canopy of your own design to these rails,
But I really think you would be wasting money, and the rails are not designed to support that stress.
For more on Fehling rails you'll have to search the internet.
They are the only company that makes rails for the Silverwing, and lets just say not a popular accessory.
You can check out a termoscud here:
http://www.tucanourbano.com/int/motorcycle-scooter-leg-covers-hand-covers/termoscud.html?brand=87&model=326
However in San Diego, where it almost never rains and people don't seem to know how to
drive when it does, your best bet is ATGATT. All the gear all the time.
Choose a windshield that best suits your needs.
Get a summer weight armored jacket for daily riding, and a rain suit that can go over your
clothes, to keep under the seat for the 9 days a year that it does rain.
The nights that it gets chilly, you can still put on your rain suit as a windbreaker.
Gloves...maybe heated grips if money is not short.
You don't get a lot of extreme weather in San Diego.
Other than the above, focus on safety upgrades. Extra lighting, mirror extenders etc.
Make yourself as noticeable as possible.
If you feel the need to communicate while riding, look for helmet Bluetooth addons.
Cell phone use in San Diego without handsfree is illegal anyway.
Dan