The Carbtune II works kinda like a mercury type but uses stainless steel slugs instead. I have one and it works very well. I ordered directly from them in England and it took about 4 days to get here. It took a letter I mailed from Texas to New York a week. It is a little expensive, about $87 including shipping.
Here is a link: http://www.carbtune.com/
Here is a link: http://www.carbtune.com/