Indeed. I check the AH and vendors basically daily looking for returning shuriken and I have never seen a slotted one available at any price or ML. At least I have picked up several made of the special metals to craft into DR breakers someday, if I can ever motivate to start leveling up crafting on my new server.
If
DDO Wiki is accurate, Seeker, Sneak Attack, Deception, and Stunning will all apply from the off hand to thrown attacks with the main hand. Deception seems like the top choice to me but you can get it (or better yet Improved Deception) on other slots.
My initial thought would be to get
Backstabber's Gloves from Crucible as those offer both Sneak Attack and Deception, a Cannith Challenge
Ring of the Stalker for Seeker and Manslaying, and then find some sort of Stunning item for my offhand. Unfortunately the options for Stunning are terrible, since it is usually limited to bludgeon weapons and there are no one-handed bludgeons that you can use and stay Centered.
However, the Cannith raids offer an option. You can get both Stunning +10 (Air tier 1) and the
Electric Storm AoE proc (i.e. the Lightning damage equivalent to Freezing Gale, Air tier 3) from a ML 12 Air-type shortsword or kama. That also gives you Alchemical DEX +2 (Air tier 2), which is great for this build. Tier 3 also offers a red augment slot, which you could slot with one of the new augments someday. This is such a great offhand option for this build that I might even get past my own antipathy to raiding to try to make one.
I think I have a something of Riposte (=Parry) in my offhand currently. I have not found anything more damage-oriented and Saves are usually worth having.