Generally your divorce settlement amount would be based on what he's claiming on his taxes. For you to try to prove that he has a lot more money could get very expensive because there's a likelihood that you'll need to get a forensic accountant.

My advice, become self-sufficient on your own rather than bothering to fight with your ex over money. I'm not sure if you're talking about child support or alimony here but if its alimony, its likely to be termed anyway and unless you're physically unable to work, the court will expect you to be taking care of your own finances as a responsible adult.

Besides, its very empowering and a much mentally healthier to be financially self-sufficient, you'll be glad you did it.