Amazingly enough, there currently are TWO Model XXXs with the upgraded bag chamber on eBay!! This is really freaky!!
In both cases, they are after-market retrofits. For a very short time, Electrolux did sell XXXs with the new bag chamber as standard equipment. That was during the very last run of the LXI when XXXs were sold as a lower-tier model. Those XXXs are all blue, hammertone blue rear collar, blue leatherette in the same style as the LX, and a blue under-carriage - ditto. The earlier XXXs have gray "snakeskin style" leatherette and dark gray under-carriages. (There's also an all-blue version of the XXX that has the original-style cover, but it's painted hammertone blue.)
Why are these replacement bag systems so rare? Not sure -- maybe many people did not want them because they didn't want to pay for disposable bags. Or maybe because they thought the things were butt-ugly, which they are! They're plain, purely functional with no thought whatsoever to form or design. And they totally ruin the streamlined appearance of the machine.
Below is a photo of an all-original late XXX [except for the go-kart -- that is a genuine Electrolux product but was an optional add-on], and then the link is to the other retrofitted version on eBay.