Where do I get JDBC drivers for the AS/400's database?

The native driver and a version of the Toolbox for Java, which includes the type 4 driver, comes with OS/400. One can also purchase or get an evaluation copy of the latest "official" version of the Toolbox. However, the open source version, JTOpen, is generally more up to date and is free.

You can find both versions from the Java Home Page. For third party drivers, check Where can I find a comprehensive list of JDBC drivers, including the databases they support?