The local Meijers, Menards, Home Depot, and Lowes stores, as well as any major auto parts retailer like Advance Auto, sell two stroke oil but I buy a quart so rarely I don't pay attention to the price. I have saved all those little 3.2 oz. bottles that came with new trimmers, etc and refill them from the quart so I have the proper amount ready to add to 2 gallons of gas. Has been a LONG time since I have seen those little green cans of Lawn Boy two stroke oil, those must be collectors items by now.
The big box stores often put two stroke oil by the chain saws and lawn care equipment section as well as the areas they sell auto oil.