1)
You can't. If you had the aptitude to do this, you would have done the research to get it done yourself by now. You can find this information if you spend enough time looking for it though.
2)
This thread has a couple of CWM flashable I9100G roms, and I'm sure there's others around the place that can be found by searching (I found this with a Google search in less than 30 seconds).