The reason you won't find this "sequence" in the CG sets is because it's not CG, it's just the normal "static" image you see of the girl in question, Miruku (say that fast and see what her name sounds like in english, noting that in this case the 'r' sound more like an 'L' than usual), whenever she's talking outside the hentai scenes.
I wrote a detailed description of the game here light-years ago, but essentially if the girls in question don't receive constant sex and milking from the protagonist due to their (imaginary but fun) condition, their breasts continue swelling with un-let milk. Henceforth how big the various girls get depends on (a) what girl's storyline you're taking part in and (b), how often they get sexed up.
At one point in Miruku's story, as can be seen if you have the CG set, she hasn't been "serviced" by you for a while, and then, when she's at her largest stage, if I remember correctly, you come down with a cold and can't see her for a few days on top of that. By the time she comes over herself, desperate and embarrased, her boobs are the size of medicine balls and are overflowing her body.
There are progression images like this for the other three girls as well, though only Miruku gets truly huge in her story.
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