By the way, I ordered this from Dell Parts through Chat service.
FYI:  I just ordered N1C1D ASSY,HTSNK,VR,CPU,125W,R11. I indicated I wanted the heatsink for my Alienware Aurora R12 part number is N1C1D. Cost is $11.99 plus tax.  Expected delivery is December 6th.  A lot less than other places.  I believe the R11 and R12 are the same.  
Aurora R12, heatsink available