At the bottom of the page, there is a link as follows,
See all versions available on the Maven Central Repository.
I have went through that page and found a previous version of Directory API Client Library for Java. By looking at it's pom i have tried following dependency and it worked.
<dependency>
<groupId>com.google.apis</groupId>
<artifactId>google-api-services-admin</artifactId>
<version>directory_v1-rev22-1.16.0-rc</version>
</dependency>
Then I tried to update the version to latest as follows and also worked.
<dependency>
<groupId>com.google.apis</groupId>
<artifactId>google-api-services-admin</artifactId>
<version>directory_v1-rev28-1.17.0-rc</version>
</dependency>