Here's a link for the square bits from Toolnut:
http://www.festoolproducts.com/accessories/aftermarket-accessories/centrotec-drill-driver-bits.html
As a sidenote I would just add, since I was doing a bunch of pocket holing over the last few days, that the best set-up I've found for driving in pocket hole screws with the #2 bit is to use the eccentric chuck and then a regular longer hex bit. Centrotec bits don't lock in the eccentric chuck. And I've found that when I use the Centrotec chuck plus the snappy square bit driver for this operation, the green sleeve of the chuck will often annoyingly will catch on the workpiece as the screw is driven in deeper.