That is generally called a spanner head screw. It is a type of security screw. To find what you need you will need to figure out the length, thread type, head diameter, head height, distance between the spanner holes, metal type, etc.
Or you might need to get a machinist with a metal lathe to turn you a new one. Sometimes old Danish hardware can be impossible to find.
In the US, these are called 'socket screws' and come in a wide variety of sizes, styles, and materials. The one in your photo is called 'spanner head' style and requires a specialized screwdriver. I very much doubt that an exact-match, new replacement can be found, but I'd recommend the McMaster-Carr website as my first choice for hard-to-find specialty fasteners and drivers.
For what it's worth, I've run into these often in my work and have fashioned make-do drivers for them by shaping 'prongs' onto standard, slotted screwdrivers using small jeweler's needle files. A little tedious, but effective in a pinch.
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