Download the OTA but don't start the update process. Open the OTA zip file which is in your sdcard/download directory. I recommend copying the file to your PC and opening it on your PC with 7zip. There is another zip file in it called framework.zip. Open firmware.zip and you will find recovery.img in it. Copy that recovery.img to either your sdcard or your PC. If you use PC, you can use the fastboot command "fastboot flash recovery recovery.img" with USB connection to fastboot. Or, if you install Flash Image GUI on your phone, you can copy the recovery.img file to your sdcard and flash directly from your phone using Flash Image GUI.