Pradeep,
The prices I have mentioned is official Canon Prices. The availability of the 500mm is indicated as May and 600mm as June. For further details check here: Canon U.S.A. : About Canon

In India, it is not yet decided when these lenses would be available. So the question of prebooking in India doesn't arise. Which lens are you planning to buy? Will let you know when I hear from them.

Cheers,
Sabyasachi