There are two Silver R2-D2 figures.  One was a vac-metal sold carded based on the 2000 Power of the Jedi figure mold.  The second was a Saga Collection figure in a UK-only boxed set with a matte finishe, based on the Vintage 2004 mold.  The set was pretty tough to get in the USA... but now you don't need to get it.

One of the many eBay sellers dealing in loose figures from Asia has it (as well as upcoming Astromechs from the 2012 Wal-Mart set) and we're just letting you know about them.