I'm thinking of getting some more orcs (Black Guard) for a good list, but they seem rare. Does anyone know where I can find some, or a good list I can use 800pts, any Mordor list?

The Black Guard models are out of production and have been moved to a legacy status. They will not be available from GW again. Your best bet would be ebay or a facebook marketplace posting.

As for lists, well, I could not say these days. The army of the great eye has a lot of options, but if you get a Morannon orcs, Gothmog, his named underlings and a troll, you should have a good shot with the army of Gothmog.

_________________
"Draw your sword with a heavy heart, but swing it with a heavy hand"