The sticker on the first photo shows what kind of lamps you can use.

From what I can see, it can use either a M59 lamp or a H33 lamp.

If you google those, a M59 is a 400W MH bulb and a H33 is a mercury bulb.

So, you just might be in luck.

Here is a link to 1 place that sells those lamps:
M400U - hid - metal halide light bulb lamp - donsbulbs - light bulbs lamps valve valves tube tubes

Try your local electric supply / industrial lighting shops in your city. You might be able to get it cheaper without paying shipping.