So far I have not found any Warrior/Archer or Rogue skills that were above level 10.

I have already my level 16 and level 18 elemental spells of all schools. But so far for anything non magic related I have seen nothing of it.

Have I missed a vendor somewhere?

The vendor in Silverglenn and the on in Cyseal only sell maximal level 10 skillbooks for Warrior/Archer.

I'm trying to think of them off the top of my head...

I think Inspire and Nullify Resistances are both above level 10.