Wide converter lense for G6

I'm going to be getting a wide converter lense for my G6 shortly. I was wondering if there are any other lenses available for the G6, not by Canon, that can make the lense pull back even more than .7x. I was going to get the Canon in the first place, but I just want to see what my options are. The adapter that I have is the 58 mm adapter.

...not sure of other brands or lens that have a wider angle but you can compare ones similar to the Canon lens at http://www.lensmateonl​ine.com/G3wideanglecon​verters.html

I have the Canon teleconverter (acts like a zoom) for the G6 and even though it was expensive, the images are very sharp when I support the camera with a monopod or tripod.