To prepare for NIMHANS in one month, you will have to be really harsh on yourself. Get any Psychiatry MCQ book (preferably Omkarnath; A book by Ahuja containing 1000 mcqs is also available). Then go topic-wise. For example - you may start with "Psychotic disorders". Attempt the MCQs on that topic , then you will have to do the text reading, so that you know exactly what is required in the entrance.You may have to sort out the MCQs topic-wise.
One important thing , find the "Synopsis of Psychiatry by Kaplan and Sadock ", and read the initial chapters on the basis of psychiatry. It will help you solve many many queries.
Then one revision at least, is necessary.
Omkarnath's publisher is -
Vikas Bharti Publishers
264/3RT, 2E, Nest Towers,
Hyderabad - 500038
Medical Book Company
Jamuna Arcade, 5-1-527Jambagh Road, Shop no. 59
Old Navrang Theatre
Hyderabad - 500095
You may also contact MBC Nagpur
They may send you the book.