@0611chaitanya...
I understand how frustrating this can be when you eagerly await for the item to arrive and then you a message that the item is "not in stock".
The fact is 80% or more ebay sellers fall in this category of listing item which they do not have, they start to procure it only when they get an order.
The reason they do not send the item to the buyer is
1. The item is not available at that time OR
2. The cost is high.
In both cases the poor buyer suffers.
Sadly ebay does not consider this as a "bad buyer experience" because a very easy way to stop this is to compensate the buyer with an ebay coupon of the equal amount. Then see how many sellers list item which they do not have in stock.
*****************