Glad to have you with us, Mackay! :welcome:
Here in Ontario there is a company that produces organic rabbit food. You need to feed it along with hay. It is mix of grains and other things like peas and roasted soybeans. The company is Homestead Organics.
http://www.homesteadorganics.ca/default.aspx
Unfortunately, there are very few companies that make organic rabbit food and even when you find one, they are usually extremely expensive.
I feed a natural diet of alfalfa hay, grass hay, whole wheat (or other grains) and as much green feed (mainly weeds) as the season allows. In winter I feed more hay and fewer fresh foods, but they always get something fresh. Sprouting grain or growing grain grass is an economical way of providing the fresh greens in winter.
I've often thought of using rabbit tractors, but they have more risks than I am willing to take with my rabbits. There is the problem of dig outs and predators. They are more exposed to summer heat and sun. In winter there is not much out there for them so for several months of snow and cold they get no benefit from the tractors, at least in my climate.
Instead, I have a small colony inside a shed, an area about 8 feet square. I pick the greens from our own land and take a big bucketful to the rabbits. The Safe Plants for Rabbits list will give you a good idea of what to bring them.
safe-plants-for-rabbits-list-t55.html
Trinityoaks has put together a grain mix that quite a few members are now using.
trinity-oaks-grain-feed-mix-t6809.html