I got the data from Intel's site. I think I downloaded it last month or so. These Product Change notifications are updated almost every month.
On the data from last month, I got following list :

B0 steppings :

S-Spec MM#
SL685 845289
SL682 846276
SL6EV 848888
SL6D8 850135

C1 steppings :
S-Spec MM#
SL6EG 848416
SL6DW 849843