Orcs don't loiter, they scourge. Usually when they are on they are spreading death wherever they can. I think their hunting parties usually muster in the desert of compassion, but our scout in that area recently had his adobe hut burn down so our reports aren't as accurate.
A very good inquiry. The npc orcs have forts in Yew, Cove and the Desert of Compassion. The Orc masks do not appear to grant one protection from attack. (I could be wrong but I've seen an orc mask clad individual get swarmed, so perhaps some testing is in order) The RPing PC orcs reside in the desert of Compassion and many of the houses and towers east of the desert. If you'd like to meet them, simply listen for the crackle of mystical energy that precedes the formation of a mystical transportation portal summoned by their shaman. Then once you've found which tower they are mounting raids from, camp out on the doorstep as they will soon gate in to the front, they will surely greet you with open arms, being very gracious hosts. My scouts have been watching them as well, but they know better than to build a hut close to their dwellings, come to think of it my scouts don't even need houses, their dead as it turns out. Having undead souls that owe you their eternal allegiance does have it's perks at times.
Actually, the masks of orcish kin work fine. I just tested it as I had always just assumed and hadn't ever tried one out.
They may be found anywhere! These were in Skara Brae,Franz and the Orcs, later that evening Franz hunted them down to the outskirts of Delucia.