[Zigûr]

We know from The Hobbit that the Orcs of the Mountains used slaves for their manufacturing purposes:
"Hammers, axes, swords, daggers, pickaxes, tongs, and also instruments of torture, they make very well, or get other people to make to their design, prisoners and slaves that have to work till they die for want of air and light."

Perhaps they produced food in the same way, although it's unclear to me where they would have found the land for such agriculture. But one imagines they could not have maintained their extensive, if petty, realms in the Misty Mountains and the Grey purely by raiding the Woodmen and so on.

We do know, however, that "sometimes used to go on raids, especially to get food or slaves to work for them." So perhaps they partially relied on raiding and partially had some subsistence of their own devising. But it does not appear that the Orc-raids, at least insofar as they are depicted in The Hobbit, were altogether regular.