CDNN has several of these LWRC 556 Piston uppers for sale at half price or better. The below link is for the one with the Skirmish sights included.
https://www.cdnnsports.com/lwrc-m6a2-5-56-16-inch-complete-upper-sights.html
https://www.cdnnsports.com/lwrc-m6a2-5-56-16-inch-complete-upper-sights.html