The way you phrased your OP, it reads as if the replacements are not available, not the shoes.

"They sell a replaceable tread kits for $38. These appear to be discontinued."

In any event, there were/are several Dragon models. Some seem somewhat difficult to find, but they are out there. E.g.:

https://www.backcountry.com/sidi-dra...mega-shoe-mens

Colorado Cyclist has the model 5 carbon if you have $400 to drop on shoes.