Canon G9 Macro Lens?

You're going to need an adapter, like so:

http://www.lensmateonline.com/store/g9.php

With that, you can then attach any number of aftermarket Macro add-ons. Lensmate is well-reputed and, understanding that they're there to sell stuff, have a look at their tests of various add-on lenses with their product:

http://www.lensmateonline.com/newsite/G7macro.html

Any decent macro add-on is going to look like a $75-125 hit to your wallet. I don't know that I'd trust something cheaper. However, you have a quality camera and I think this would work well for you.