Greetings Marshall:
Like all tree species recommendations, tree selection should be heavily weighted on the basis of your soil texture, soil pH, soil moisture, and other site specific factors (next to a road, house, etc.). Without a little research on the homeowner’s part, an unfortunate result of planting a tree that is not physiologically adapted to the site can inevitably lead to poor tree health and vigor.
With that said, please take a look at the following Web site to assist you in making this decision. Several native conifers you might want to look at include northern white-cedar and eastern white pine.
http://www.urbanext.uiuc.edu/treeselector/
Regarding where to buy the tree, please check your local yellow-pages for a list of nurseries in your area. You can also contact the Illinois Green Industry Association http://www.ina-online.org/
Best of luck!