It was available at this support link below if you look under drivers and tools and then select firmware but it looks like they removed it. Only goes up to 2.18 now. Plus you have to choose cn or ww version. Confusing but here is link.
OTA not working any more for mine, a WW version. Other updates did work fine. Had to download this from the website and place it in root of internal SD folder. After restarting the phone acknowledged it and updated.