Natural product to unblock outside drains? Thanks?

There are enzymes that contain bacteria that will eat some of the waste, but it's for preventative maintenance. It won't eat through a solid clog, at least not in the time-frame that most people would want their plumbing to work.

I would try to run a water hose at full flow down the drain line.

there are no natural chemical means. mechanical means will be best in many cases ( rodding etc) .otherwise we need specialised gear such as high pressure water jetting.