The Finetec Pearl Metallic Ink Palette is by far the best out there. Fantastic shades and very long-lasting.
Individual palette refills are now available. Colours available (clockwise from top left): Tibet Gold, Inca Gold, Moon Gold, Arabic Gold, Gold Pearl, Sterling Silver.
Made of mica, a natural mineral that offers a wide variety of metallic shades, from gold and silver to iridescent, shining pearl colours. Activate with a little water on the palette and apply to the nib with a brush. Adheres to all absorbent surfaces, such as paper, wood, gypsum, etc.
(There are tons of forums, links and youtube videos that show you how to best use this product. Here's one we like: http://www.aninarubio.com/blog/2014/11/4/mighty-mighty-finetec)