U can easily access PDF of ncert class 9 an 10 books and also u must read the related topics from the icse textbook.

Or u can get the study material of some institutes like Allen, motion and all through dlp.In a day along with the icse syllabus you must take out a minimum of half an hour and study for ntse.

Feel free to ask me in the comment box if you are having any further doubts

hope you find it helpful

Good Luck!