my girlfriend just bought a soft case for her DGX 220 (the same model, i've no idea whats de difference between a 230 and a 220, but they look exactly the same) frm yamaha PS like a month ago.
just ask them for it,
cos what you see lying around the place are soft cases for 61 keys, but if you ask, they may have stock kept somewhere for the 76 keys, and it fits JUST nice, just right exactly for her dgx 220. =)
but because its just nice, there's no space nor pockets to put ur cables, dc adapters or pedals anything, you'll have to carry them separately if gigging with it. =)