Why can’t I find natural beans easily? I usually buy my coffee from dark arts, ozone, climpson &amp; sons and workshop. 

I usually buy natural as I feel it has more flavour than washed and is better with Moccamaster. 

Why am I struggling to find natural lately? Is it out of favour? I can’t find natural at any of this places anymore.
Consumers (and marketers) are expanding their vocabulary for describing coffee. And at the same time coffee producers are improving and refining their methods. Both of these I think contribute to what you're seeing. 

The term "natural" process can be ambiguous. You might try to search on a more specific, technical term "Dry Process," usually a synonym for natural process. Here's some dry process green offerings from Sweet Maria for example. 

As for processing, dry process is going out of style in favor of the (technologically speaking) superior wet processing techniques. Wet process allows better removal of defects (bad seeds) and other benefits for making higher quality and more consistent product. As you note processing has impact on flavor. Wikipedia has a good overview of different aspects of coffee production, and roaster web sites like Blue Bottle have overviews with their philosophy. 

Ethiopia and Northern Africa tend to use dry process more often than other regions, due to the dry environment conditions well suited for the dry process. You might focus your search on beans sourced from that region.