I'm still not sure to understand everything (things might be obvious for you but believe me, they aren't for the readers) but this looks more like a Subversion issue than a Maven issue. Maybe Externals Definitions could help here:
Sometimes it is useful to construct a working copy that is made out of a number of different checkouts. For example, you may want different subdirectories to come from different locations in a repository or perhaps from different repositories altogether. You could certainly set up such a scenario by hand—using svn checkout to create the sort of nested working copy structure you are trying to achieve. But if this layout is important for everyone who uses your repository, every other user will need to perform the same checkout operations that you did.
By setting svn:externals
properly, it should be possible to fetch everything from various repositories with a single checkout.
For more guidance, post a more precise question :)