Does anyone know a source for replacement brass nuts for the spirit nut effect? Ungimmicked, genuine nut.

There are at least 30 different manufacturers, over time who have made this, so unless you measure the outside dimensions, the size hole and the threads per inch...

Not to mention weather it has a chamfer and not to double mention weather the material is an alloy or has impurities which may determine the color....

Go to your local "Do it Best Hardware" store, and look in their specialty boxed section for fasteners.

You may find a nut similar to yours. As Jay Leslie said, you will not get an exact match, as these have been made by many different companies and countries over the years. All were different sizes. That is why they come with a matching nut.