Short answer: there is no easy way.
Schema-derived classes have no reference to the original schema anymore. Even if you use something as XSOM or whatever to parse the original schema, you will not be able to find corresponding XML Schema constructs to check.
The best way to address the issue would be writing a custom XJC plugin (I wrote quite a few of them).
When XJC compiles the schmema it first creates a model, then a so-called outline (pre-rendered code) and then renders the code. The model still has information about the original XML Schema constructs, so you can find all the relevant min/maxOccurs information there.
The problem is just that you don't always have 1:1 mapping between schema constructs and properties of schema-derived classes. Sometimes several elements are mapped onto one property. There's a huge number of exceptions and special cases. You can get it working for the straightforward cases, though. Anyway, the task is not easy.