I've been looking all over, but can't seem to find any info about this.
The armor from Katta Castrum merchants has this aug slot plus a type 7. The only items they sell that are type specific are power sources, which are type 1, and I assume these go in the inventory slot, not on the armor.
So, what's 13? Player made?
"An assassin is chaos unleashed..." - Steven Erikson
13 and 14 are designed to be for Purity increasing Augs which were to be found as zone rare drops. I'm not sure if the plan is still to add them with TBS or with SoF. I do not know of any type 13 augs currently in game.