What alloys can be used to make a metal pencil like this one?
"Silverpoint" nibs have a long history in art and significantly predate modern drawing tools such as the lead pencil (made of graphite and clay but possibly called lead as lead metal was one possible material in metal pens). Silverpoint writing and drawing doesn't smudge or fade and many examples have survived almost unchanged over hundreds of years.
There is a useful site with a good history of the original artistic uses of silverpoint pens here. According to this site a wide variety of metals will work. Historically which was used depended on status:
Wealthy and royal persons who needed to keep records (business inventories and so forth) employed these scribes, and the stylus material served as notice to all of the status of the employer - gold and silver for the upper classes, lead for somewhat lesser beings.
It seems tht many metals will work. The dictionary of Art is quoted as saying:
Metalpoint. Drawing instrument (the forerunner of the pencil) made from a small, pointed metal tip, usually of lead, silver, copper or gold, encased in a wooden holder.
The current preferred metal for artistic use seems to be fairly pure silver.
Best results are obtained from a thicker point that is "pure" silver, or ".999 fine." This is much softer than sterling, so it will deposit more metal on the drawing surface
The silverpoint.com web site sells ready made points of both silver and gold.
It isn't obvious what metal or alloy is used in the pens mentioned in the Wired story, but it isn't silver. It apparently contains at least some lead as the pencils come with warnings not to let children chew them!
I actually make metalpoint pencils and use pure lead for the writing material. It's obviously a bit toxic (because lead), though I'm experimenting with making custom lead alloys (possibly with a percentage of bismuth, as I have some laying around) to reduce the overall lead content. In terms of utility, however, pure lead leaves a reasonably dark and easy-to-make mark.
It could be similar to "Lead or Aluminum Metalpoint". For instance, I use the 2.4 mm and 1/8 inch "soft aluminum" rods obtained in the US from Hobby Lobby in a pack with two of both sizes (about $4 USD). The smaller rods are placed in my drafting technical pencil holder (Koh-I-Noor, 2 mm still works). I use an old wooden brush handle drilled to 1/8 inch diameter hole, for the larger rods. A strong gray/black line is obtained when using "Rite-in-the-Rain All-Weather Sketchbook" with no further "silverpoint" ground treatment. My "Lead solder' (Home Depot/Lowes) stylus works on regular paper with none of the usual titanium white ground treatment.