If you have any experience in fabrication, you can do this yourself. Try making your blank in the maximum dimensions of the existing nut, then stick it in a vice and take a mill file to it. Once you have the top contoured where you want it, use a scribe to start the string slots (I prefer to start any slot by making a mark with a nice, sharp exacto blade). Then a round needle file, or possibly a torch tip cleaning file set (good tip from Bloozcat) to shape the individual slots. In fact, now you got me thinking... what about copper (very easy to cut)? Titanium (very, very hard to cut)? Tungsten carbide (good luck...)?
