Kosher Food

To be honest I don't think any mess hall meals are kosher, I am sure that the Jewish chapel serves kosher during their services but I can't think of anywhere else off the top of my head that you could go to get kosher.
how easily can Jewish cadets get kosher food?

I know back in the late '90's King Hall at USNA was able to make special kosher meals for the jewish midshipmen. Your best bet would be to try and contact the rabbi at USMA.
Kosher meals are not served in the Mess Hall. You'd have to come up with your own way of doing "kosher style". During Passover, there are separate kosher-for-Passover tables and meals prepared for Jewish cadets. Meals at the Jewish Chapel are kosher. Rabbi Huerta would be a great resource.

If you are in the area or are planning a visit sometime soon, plan on attending Friday night services. Except on very snowy days (when it's too hard to get up the hill) the attendance is very good.