In SAP MDM when we create multiple repositories in landscape there is no standard way through which we can make data exchange possible between two repositories
There is no standard approach to meet this requirement, but this can be achieved.
In our project there was a similar requirement where we have to make sub tables of two different repositories communicate with each other i.e. if either of the sub-table is updated or new record is created the changes should reflect is sub-table of other repository too.
Now the approach goes like this, we would create an inbound and outbound port for required repositories, we would use an UNIX scheduler (Since our MDM server is installed on Unix System) to run a script which will move xml files (updated Data) from outbound ready folder of one repository to the inbound ready folder other repository.
Using this approach we were able to pass data from one repository to another.