JAR files referenced by custom defined user libraries in Eclipse are indeed not exported along the project when you choose "Export as Eclipse project" option. The importer is supposed to have the very same user libraries in its Eclipse environment.
You have several options:
Create the same user libraries yourself.
Use "Export as WAR" option instead. Eclipse will include the libraries in
/WEB-INF/lib
.Manually include those JARs in project's
/WEB-INF/lib
yourself.