You can buy all the "Quick Change" parts for a regular Uniflow directly from RCBS. That includes the 2 bigger hopper options the Quick Change has.
Midway sells all the Quick Change parts to convert a regular Uniflow....except for the hoppers. Go figure. You have to Go direct for them.
BTW a new Video from RCBS shows how dang easy it is to change hoppers. (This video is about 40 years late!) Once you get to the link, go down the column to video 13.
(Remove and Replace a UPM Hopper)