Regarding the actual ounces, I have not tested my large or small glasses (those are the two "sizes") but I would guess that the large is a 16oz filled to the brim and the small is a 10oz. That would directly correlate to their pour sizes of 14oz and 8oz. Just my guess.
No...the orange was only made/sold in one size. Not sure about the new Red/Purple glasses. They are a different glass all together (not Stolzle glass anymore, something cheaper and thicker). As far as I am aware they are only one size.
No, only at the bar. And even then it seems they aren't really for sale. Have to talk to the rightught person it seems.