So I've leveled a Sith Marauder to 36 and a Jedi Shadow (DPS) to 26, and I've noticed the same problem on both toons. The commendation mod vendors (and to a lesser extent the regular mod vendors) seem to hate DPS specs. For both the Sith Warrior and Jedi Consular classes there's two types of "useful" gear mods. For Consular there "Force Wielder" which is heavy endurance and a bit of willpower, and "Resolve" which is heavy willpower and a bit of Endurance. For Sith Warriors there's "Guardian" and "Might" which are strength and endurance the same way. Clearly the Force Wielder and Guardian are "tank" mods and Resolve and Might are "DPS" mods (also healers probably use Resolve, but I don't have one so I'm not sure).
The problem is that at pretty much every mod vendor I've come across there's two-three levels worth of "Guardian" and "Force Wielder" stuff, in Hilts, Armoring, and Mods. There's usually only one level (always the lowest level the vendor offers of the tank gear) of "Resolve" or "Might" stuff, and often it's only Hilts and Armoring, no Mods. My SW can make hilts and mods, so it's slightly less of a problem for her, but my JS is biochem, so he's constantly behind the curve on his orange gear. It's still better than what you can get in greens or blues generally, so I keep buying the inferior stuff, but am I missing something? Is there somewhere to get the DPS mods at the same level levels you get tank mods for a similar cost? Am I just supposed to use tank mods while leveling?
It's been driving me kinda nuts.. Every time I hit a new vendor I hope that this one will have the gear I actually want, but so far I've been disappointed (also no one really seems to sell low level mods on server in the GTN).