This is my current army with 425 points. I want to reach 1000 points. I can ally some other units from Mordor or Isengard but I want to build a pure Moria army. What would you suggest?

1 Shaman 12 Goblin Warrior
1 Captain 10 Goblin Warrior 2 Drummer
1 Shaman 2 Goblin Warrior 1 Cave Troll

Well moria has lots of good options for a pure moria list luckily, I would start adding prowlers to each warband, they are amazing imo, f3 (helps with the gang up mentality against non elite foes) throwing weapons on a 4+ (or bow of you so choose) or my more favorite load out is the two hander, get someone surrounded, put all your prowlers on 2 handed piercing strike duty and watch them rain 2 - 3+ to wound rolls on those poor souls.

The next unit I would strongly (real emphasis on strongly)
Consider is warg marauders, easy to convert up, and just a superb cav model that functions like no other, a pack of a few will show some divends on really crushing isolated foes or slamming flanks (they also skirmish fairly well by orc shooting standards,but imo too expensive for that duty primarily)

Also consider changing out the 2nd shaman for another captain, I'd only take a shaman at every 3rd warband or so (so your not starving your might too badly, for redundant/ overlaping use of fury)

I second the above.

On top of that:
-Durburz
-Bat Swarms
-more Cave Trolls
-Spider Queen