I'm not sure if this link will work or not, but essentially it's a video from PBBA (Professional Big Bore Airguns) showing their 20gauge PCP shotgun, how shells are loaded and and how to insert their .457 rifled barrel. I haven't found any mention of price, or how to order, other than calling AirHog though.
https://www.facebook.com/renee.bousquet.3/videos/969049399824072/
https://www.facebook.com/renee.bousquet.3/videos/969049399824072/