They simply forgot to add them when they changed us tank assasins from str to will at one of the betas. I am an artificer aswell and would love to be able to make an offhand I can use, not just ones my companions can use. Been using quest rewards and BoE versions as much as I can, thankfully my guildies have been nice enough to save them for me when they come across tradeable ones. Other than that, I guess your best bet is to stalk the GTN. Hopefully they add them at a patch sometime soon, I would not hold my breath waiting tho.