In 1888 physicist Heinrich Hertz set out to scientifically verify Maxwell's predictions. Hertz used a tuned spark gap transmitter and a tuned spark gap detector (consisting of a loop of wire connected to a small spark gap) located a few meters away. In a series of UHF experiments, Hertz verified that electromagnetic waves were being produced by the transmitter. When the transmitter sparked, small sparks also appeared across the receiver's spark gap, which could be seen under a microscope.
Spark-gap transmitter - Wikipedia, the free encyclopedia
A gap which is the correct length in relation to the power of the signal and the wavelength can produce a spark across the gap. It's technically possible, but as you said, hasn't been spotted in the wild yet.