I cannot add Common Core grade 5th Math to my student's class created on Khan Academy from India.

Hi Kamal,
 
The courses shown in a class's Course picker are curated based on your location. That said, you should still be able to look for those courses and manually assign content from there to your class without the need for the course to be added to the Class subject line. You can do this by following the steps lined out in the "Assigning them while viewing the content item itself " section of the article How do I create assignments?

Now, if you'd like to set the courses aligned to the US curriculum to your class, I'm afraid you must use a VPN and set your location as the United States— that's the only way you can change your location at Khan Academy.
 
Finally, I’d also like to recommend our course, Khan for Educators, too! This is a dedicated course for teachers getting started at Khan Academy. It’s composed of seven lessons that explore everything from getting started to classroom implementation and diving deep into Khan Academy’s teacher reports.
 
I hope this helps!