For a black 7-string nut I'd look on eBay. e.g. http://www.ebay.co.uk/itm/GRAPHTECH-...kAAOSwsXFZM-Ra

But measure the width of the neck first (and also the existing nut height) to avoid selecting something too small or too big. Graphtech do a lot of nuts so it's worth looking at their website, selecting the one that's the best fit for your neck and then Googling for the part number. Someone will have it in stock somewhere. http://www.graphtech.com/products/pr...ategories/nuts

As you want black, then I'd definitely recommend something like their Tusq nuts over a standard plastic one. Well worth a few Euros extra.