TIBCO has a separate installer to get DataDirect JDBC drivers with TIBCO Runtime Agent (TRA) version 5.7.x or higher. You will need to manually install the DataDirect JDBC drivers('TIBCO Database Driver Supplement Software 1.x.x or higher) from the Tibco download site https://edelivery.tibco.com .
NOTE:
1). Drivers will get installed under <TIBCO_HOME>/TPCL/<version>/jdbc.
2). TIBCO Database Driver Supplement Software is available under the TRA tenant products, e.g TIBCO BusinessWorks(BW) or TIBCO ActiveMatrix Adapter for Database (ADB).