Coffee producers tailor their production to worldwide demand for coffee. Wet processing of coffee produces large quantities of green coffee bean for the lowest production cost. The process is more automated and satisfies the world's demand for low cost coffee. Dry processed (what you are calling "natural") coffee is the oldest processing method since it doesn't require large volumes of water, and compared to wet processing, is time consuming and labor intensive. The resulting beans therefore tend to be more expensive. Unfortunately it seems that people value low cost over quality coffee, at least on a mass consumer scale.
I drink exclusively dry processed Ethiopian coffees, mostly Yirgacheffe or something from nearby. They are indeed slightly more expensive but since I roast my own beans, the cost is still quite low compared to buying roasted beans at full retail price. You are correct in noticing the relatively scarce offerings of DP coffees, but I source my beans from several different online sellers, and am usually able to find at least one with a current Ethiopian DP coffee.
I would encourage you to also search for "dry process" or "DP" coffee, in addition to "natural" since there really isn't very good standardization of terms across the industry. I should say that I began roasting my own beans only after I found how much I liked dry processed coffee and how hard it was to find, so I completely understand your frustration. The upside to roasting my own was that it's guaranteed to be fresh, a critical part of really good coffee. Good luck!