When you define a bean in one of the package bean definition files you simply set a dependent bean from another package on each bean definition.
This results in packAbean being DI with the bean from packB. Of course, this assumes a very simple environment, that the bean definition files are combined or in a hierarchy, for the bean ref to work. No getBean calls in the code are required.
<bean name="packAbean" class=".......packA.PackABean">
<property name="packBbean" ref="packBbeanName"/>