I just recently started practicing for my MATH GRE which probably towards the end of this year. I'm an international student who spends roughly half his hours online.
I just had a look into the questions in the Mathematics GRE Subject Test Books by Princeton Review and ETS. The problems and questions seem to be very similar both in syllabus and difficulty to standard problems in the IIT-JEE examination. For those indians preparing for the IIT-JEE, I'd advise you guys to pickup R.D.Sharma, Last 25 years IIT-JEE papers etc. Those books should give you a greater amount of practice (seeing that each of those books have > 10000 problems spread over similar syllabus).
Try to get such books if you run out of practice questions.
Weird analogy: Why do they ask 12th grade stuff(India-wise) in a test which partially determines admissions for a Master's program in USA?
I would have thought that they would at least ask linear/non-linear optimization/operations research questions.