I receive a driver not found error using the URI and when I point to the derbyclient.jar file
You have placed the .jar in your Java CLASSPATH (<fme install>/plugins would work in a pinch), and have specified the Driver Class Name as org.apache.derby.jdbc.EmbeddedDriver in the JDBC format settings box? (I assume you are trying to use the driver from https://db.apache.org/derby/docs/10.4/devguide/cdevdvlp40653.html)
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