OWL ART API (and all its distributed implementations for existing RDF technologies) are mirrored on Maven central, and can be automatically imported from there when using Maven for managing your software projects
Maven bundles (containing binaries, javadocs and sources for both library and test suite) for various versions of OWL ART API are also available from its project site on BitBucket.
Packages containing OWLART, its sesame2 implementation, all related dependencies and some sample batch files for using their CLI utilitities are also available from the same page. They are exposed in the form: owlart-<version number>-dist
Downloads for versions up to 2.0.4 are available on the old google code project site
The source code of OWL ART API is available via GIT from its project site on BitBucket
Sesame2 Implementation of OWL ART API is available from its project site on BitBucket
Allegrograph Implementation of OWL ART API is available from its project site on google code. This project is not maintained, though you can easily update it to reflect dependency on the latest owlart-sesame2 and on the allegro graph client you need for your installation