Assuming you already have the external amps available to maven (either because their're on Maven Central repo or because they're installed locally), you simply add the external amps as dependencies in your amp project. E.g.:
<dependency>
<groupId>org.sharextras</groupId>
<artifactId>javascript-console-repo</artifactId>
<version>0.6.0</version>
<type>amp</type>
</dependency>
You also must configure the maven dependency plugin. You can do it in a profile so it can be turned on or off depending on your needs:
<profiles>
<profile>
<id>unpack-deps</id>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
<execution>
<id>unpack-amps</id>
<phase>prepare-package</phase>
<goals>
<goal>unpack-dependencies</goal>
</goals>
<configuration>
<includeTypes>amp</includeTypes>
<outputDirectory>${alfresco.client.war.folder}</outputDirectory>
</configuration>
</execution>
</executions>
<dependencies>
<dependency>
<groupId>org.alfresco.maven.plugin</groupId>
<artifactId>maven-amp-plugin</artifactId>
<version>3.0.2</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>
</profile>
</profiles>
This way, you can start the main project amp plus its dependencies with the following command:
mvn integration-test -Pamp-to-war -Punpack-deps
For a complete pom.xml example see: https://github.com/douglascrp/alfresco-value-assistance/blob/master/alfresco-value-assistance-repo/pom.xml