Take a look at the attached cut away drawing from the Sept 1972 issue of Air Enthusiast.
No oxygen system is shown, not even the circular oxygen regulator you see on both US and German aircraft (note, we copied ours from theirs). Now, think. It had a very short flight time and utilized a spring loaded ejection seat. The pilot had to wear a special suit from protection from the rocket propellants. My conclusion is that the pilot carried his own oxygen bottle and regulator, which acted as a Bail Out Bottle as well as helping him being protected from the highly hazardous propellants.
Note that no oxygen system is shown in the cut way drawing of the Natter as well. Same reason.