They're a thrift store find. The last pic shows six. They wrapped masking tape around them! I kept one from one side. I did my best peeling that tape while trying not to damage the cardboard, ..it peeled the skin in some places (shown in 2nd picture). It's still structurally sound. It did no damage to the filter element. There was no tape stuck to the others. Just the two on the outside, I kept one. There's no evidence these have been used. You can tell they're brand new.
$30 gets them all ..thanks.