Disclaimer in honor of my Irish Ancestors:
I wouldn't dare to serve kimchi as a St. Patrick's day dish for fear of retribution from beyond-the-grave! :W
That said, and per every other day of the year:
I'm a kimchi lover, too and can verify that ordinary green cabbage is a poor substitute for the traditional Napa. On the other hand, Napa is a poor substitute for green in uses like stuffed cabbage rolls (or corned beef and cabbage), so it all evens out in the end, eh?
My favorite recipe for homemade kimchi is the one found at
this site. That's for the traditional "whole" kimchi, but there's also a recipe at that site for the easier
cut kimchi. Both recipes call for the critical key ingredient of rice "porridge", an essential nutrient for the bacteria that gives the unique flavor to authentic kimchi.
FYI:
The fermentation process is greatly impeded by refrigeration. I keep fresh batches in a "cool" place for at least a few days before refrigerating to slow down/arrest the process.
The site above also has TONS of other recipes/how-to videos for all kinds of other Korean dishes. :)