JaysonBlade has a bunch of very nice comics featuring breast expansion themes. They’re usually six panels, with the object starting out as having small but perky breasts. Soon she’s growing, her clothes splitting at the seams or the buttons, and then blowing completely apart as her newly-gigantic breasts balloon out, each much bigger than her head.
Anyway, you know how this works. Click on the image above for a link to that comic, and then on JaysonBlade’s name on deviantART for more breast expansion comics.