A floppy hat with a "brim" all around can help. You can shape it to suit your need. With a cap, with a bill, you can position it to the left or right to help block the sun.
You can serve from different positions on the court (within reason) to avoid looking driectly into the sun.
You can turn your body in relationship to the court (sort of like the McEnroe serve) to avoid the sun.
You can adjust your toss.
You can get glasses that have lenses that flip up and then leave them up to act as a sun shade.
You can have a ball kid hold an umbrella on a stick to block the sun. Check the rules on this one first.
You can buy 300 lbs of dry-ice and mix it with water in a machine that creates a cloud-cover on your side of the court.
You can fly out here to the Central Valley in California, where we live in constant gloom.