Sorry if this is an old, tired topic. I'm new to the game and want to build a force comprised mostly of vanilla orcs and ringwraiths. Are they really unviable? Should morannon always be the way to go? What if I don't like the black guard or other troops that didn't show up in the movies? I mostly want to slap down a couple dozen orcs, support them with magic and the occasional troll, and humiliate the myriad fools among the free folk who fancy themselves as heroes. Thanks for the help!

I think that the Barad-Dur army bonus was actually thought with the "Morannon over Mordor orcs philosophy" in mind. Said bonus grants models from the Barad-Dur army list (which doesn't include Named Wraiths, Gothmog, Morannons, Black Guards but includes trolls)a +1 to wound a outnumbered opponent. And Mordor Orcs can be spammed.
Common Ringwraiths are good spellcaster too. I believe that, expecially with the army bonus, it's absolutely viable

Where can I find details on the Barad Dur list? Is there Mordor sourcebook current?

Here:

https://20889-presscdn-pagely.netdna-ss ... -Rules.pdf

is a list of additional rules for army bonus tested during the Throne of Skulls event. However, they are yet to be made official