Dear Swapnil,
As per my assumption we have two options.
1. If different assembly have different storage location, then activate MRP area, and run MRP with MRP area wise(i.e., storage location wise). So purchase requisition will create MRP area wise deficit quantity.
2. you can use Make to order scenario. In material master make the Strategy group as 20 (Make-to-Order production). Then run the MRP. Order wise purchase Requisition will be created separatly as per the demand quantity.
Regards,