I didn't find any exact solution. Perhaps because of the voltage problem. Sony L-series batteries are 7.2 volts, and the Zoom H4N wants 5 volts. It might be possible to make a "LDO" (low drop out) voltage regulator to get 5 volts from a 7.2 volt source, but it wouldn't be very efficient, especially with those expensive Sony batteries (vs. common AA cells).
And, yes, there battery plates available for Sony L-series, but they put out the 7.2 volts from the battery, and like most Sony accessories, they come at a premium price.