This may just be a glaring oversight on my part, but I have not been able to find recipes for defensive mods. Particularly the str/end mods. Have I missed them or are they not available ?
As stated, it's (arguably) a bug. There are no schematics available for them, but you CAN get them from various dailies/etc. So they DO exist. One of the arguments why, particularly for tanks, crafted "finished" armor is generally superior to custom modified armor.