You can't use a pair of single pole AFCIs. There may be a 2 pole AFCI that will handle a multiwire circuit but I haven't seen one.
The AFCI has pretty much made the residential multi wire circuit a thing of the past. Using more copper is probably cheaper than the 2 pole AFCI to serve it.
(or so Schnider says)

http://static.schneider-electric.us...t%20Interrupters-AFCI/0760DB0203R902.pdf

Cuttler Hammer may have a "classified" AFCI breaker that is listed to fit in a SqD panel. I will not start that argument here wink


Greg Fretwell