You can currently purchase magnetic polish from LCN, which sells 8 shades at under $10 each. You have to purchase the magnets separately for about $20. You can get a star or a diagonal line.
The UK-based Nails Inc. company will release a new polish in October named Magnetic Attraction. The colors come in 3 shades -- gray, gold and purple -- and the magnet embedded in the cap allows you to create cool ripple effects.
You can see more photos on the Vampy Varnish blog.