I still wouldn't rule out the possibility of feather mites. Just because others show nothing doesn't mean they are not there. Not the easiest bugs to get rid of. They live on/in the feather I think.
They are called pinless peepers. They have them in plastic colors and basically they just hook on the nostrils. I used them once. You need to make them bendable by warming in hot water first, and then someone holding the bird and it's head still while you try to bend them into place helps.