They are not "hex code" they are called ID (well if it's what i think you're looking for)

Fire Flame ID : 4430
Water Flame ID : 4835

ingame do

lf 1/0 (uke or tori) 4430 4835

then wait til your game download the flame and then it will appear, try it on single player if it don't appear directly when the download is done space a bit and it will appear.