I understand the "we don't have those." I might have words for someone bold enough to tell me what I could/couldn't buy.
I believe what they are trying to say is that peanuts and cashews don't grow well in your area. I've never heard of a nursery not selling a crop because people make too much money off of it. Usually they will sell anything that grows in your area. But, that's just my experience. I don't know where you live or what the situation is.
Here we can't grow citrus trees. They just won't grow outside. I do know of someone that successfully grew a lemon tree on her back porch, but it required a great deal of care and put out very little fruit. She did it because someone told her it couldn't be done.