Personally I chose local over organic but I have been buying/growing/eating locally raised foods for over a decade plus I an a small commercial grower who used to be certified organic so I probably have a better handle on this subject because I live my life around it.
First off buying local is not easy and demands that you think about food differently. If you want to eat in the winter you start planning in the spring. Ideally you will be growing quite a bit of your own food and buying the rest via farmers market and individual farmers who may not go to farmers markets. Especially if you are not finding locally owned stores with locally raised food. http://www.localharvest.org should help you find and connect with local growers in your area (there are many sustainable and organic growers in Montana but it is a big place so I can see where it would be hard to find who you need to buy from)
You need to put up food by canning, freezing, fermentation, dehydration during the growing season for use during the off season. And create a root cellar for foods like garlic, onions, carrots, turnips, winter squash to be store in. This is what people used to do before WWII and the modern, processed food, grocery chain.
The book Root Cellaring by Mike and Nancy Bubel is an excellent title on the subject. they explain how anyone can do this even people living in apartments in the city.
The other thing to do is if you are gardener yourself learn about season extension. I know people who grow most of the year in Minn and S Dakota using simple unheated hoop houses. Eliot Coleman has several excellent title on season extension, he lives and gardens year round in Maine. I know of a couple of farms in MT that use geothermal hot springs to heat greenhouses for year round growing in your state so it can certainly be done.
Keep on educating yourself and good luck. I believe you can and will become a full fledged Montanan locavore.