Where to find graduate scholarships for international students?

My son is applying for MS in United States. Where can he/I find scholarships? And, who is eligible? any criteria?

Besides, I would like to ask few more questions.
1. How many scholarships can he apply for?
2. Can he apply for both scholarships and assistant-ships (RA/TA) at the same time?
3. Is spending so much on graduate studies worth it?
4. I want him return back after he completes graduation. But he insists he will return, but after gaining some work experience. I would like him to marry and then work if he wants after graduation. Your opinion?
5. Can he get a job after graduation there?
6. He says his field of study is new to our country, so he will bring in that after studying, and thus can get a job here afterwards. He adds it will be easier to find a job here if he gains some experience there. How do I know it will be so?
7. Are scholarships available only to specific fields of study?

To clarify, he is not national of United States, and hasn’t traveled abroad before. He has completed bachelors in mechanical engineering. And, he wants to study operations research for MS. I am telling him to apply to both operations research and industrial engineering. If you please, can you answer same for other fields of study too? Following are fields.
Mechanical engineering, fluid and heat
Computer Science
Biology
Animation