One to many - many to one with four tables

[frankb3]

I have successfully built a one to many relationship between two tables called Orders & Stations, with a 3rd table called order_stationlink where an order may sometimes have more than one station on the order at a time.

Now, enter a fourth table called PSA's.  It's separate set of data that is processed a little differently - and that will be brought into the main Orders table later.  But instead of a field called Station, it is a field called Region, which may include one or many stations at a time.   What I'd like to do is be able to pull in all the Stations that belong to that Region, and somehow move that data over into the Order once the PSA is ready for submission.  Appreciate your help.