Issue Run MRP for a Single Order
Solution

U will have to set Reservation "Always" on both component and FG. OnSales order use Order Promising after accepting the capable to promisedates ur FG line would be visible on Planning Worksheet inManufacturing. Now on Planning worksheet run accept action message itwill bring the MRP for the line above. And it will be for only thatorder only. 

Make sure u have Tracking & Action message set on both item cards as well.

OR

Just check critical on RM and run Order promising for FG. Once u runcapable to promise it will bring all the stuff without any setting onMfg Planning worksheet. Easy and hassle free it would be.