We've got some Orc Raids among Tibia, but only from raid on Fermor Hills you can loot Amazon Set.
We also got a huge raid near Thais Gates, but as far as I know it is still not proven that we can drop Amazon Set there. It is announced:
0.00: Orc activity near Thais reported! Beware!
00.07: Thais is under attack!
00.09: [last wave with Orc Warlords]
Raid on Fermor Hills is unannounced and there is only one, big wave.
I remember when SeikatsuTV wanted to cheat on TibiaBosses' The Great Boss Hunt contest and sent us Amazon Armor from Orc Warlord from Thais raid - CM said this ss is a FAKE.
Both are once a month, but exact time is random.
Unannounced raid near Thais Lighthouse works in a completely different way and there is no chance to loot there any part from Amazon set. It appears once per week.