I built a self-ballasted MV light about 10 years ago. I bought two 500 watt bulbs (which I still have) for $15 a piece online. It still works great.
These days I cannot find a bulb anywhere. NOWHERE!!! This is due to the previous administrations regulations on light bulbs to "save" energy. So I know I will never be able to replace my bulbs in the USA once they are gone.
You must look at companies that done stock in the past and use today another kind of lamp (public lighting, administration, factories etc.). In traditional stores you will not find them, except some that stock them in the past but it becomes more and more rare.
It becomes late to stock for the rest of your life .... I am not confident in Led technology to replace it.
s'il n'y pas de solution c'est qu'il n'y a pas de problème ! akuna matata ....