The /export trick is fantastic. Just make sure to get the initial URL from My Flows, not from Solutions, as the GUID is different from Solutions, and you will get a resource not found error (if your URL ends in "/details?utm_source=solution_explorer" you're grabbing it from Solutions).
If you have a lot of flows, and haven't edited the one you want to export recently, you will also need to scroll down and click Show More. Unfortunately the Search gadget only searches the context of items currently displayed. Alternatively, from Solutions on the left, you can export all the flows in your solution in one go, but the folder structure and resulting JSON is different.