When you see breweries (especially in the US) using shapes or sizes other than the normal 750ml it's because they can special order large enough volumes that their wholesalers can place orders. Homebrew shops generally sell so little of that kind of bottle that the wholesalers tend to only make the most basic size and shape available. That's generally true for brown bottles, too. Usually you only see a traditional 12oz long neck. At the peak of sour beer in the mid-2010s you could occasionally find shops willing to arrange purchases of the other sizes or shapes at a steep markup. At that point you might as well just buy a couple cases of a beer you like and have a good time acquiring empty bottles.
Champagne style bottles will accept cork and cage if you want but they are a different size cork from the mushroom-style Belgian bottles. Many homebrew shops also sell green bottles with a 26mm mouth (typical beer bottle size) instead of the 29mm (typical champagne style bottle) so make sure whatever you get you either have the right size caps or corks. You can shatter bottles forcing in corks that are too large. You run the risk as the corks swell shattering days or weeks after you bottle. I'm sure somebody will come in to disagree that they use the wrong size all the time but you can search for threads here and find enough people who had less luck.
