I have seen a number of people want to know if they can form Greece or Prussia. Now I can say yes without making them dig through a mod to find a simple event for vanilla!
These are very simple events that are only meant to let them be formed in semi-historical ways. (I also see no need for them to be very complex or needing to be completely historical)
Greek event: http://rapidshare.com/files/214660904/greeknation.txt
You just add the events into your Paradox Interactive\Europa Universalis III/events folder (Wouldn't recommend this)
you add them into the events folder of any mod. (Recommended)
If you don't want to mess up your vanilla checksum and use these events with the rest of the game being vanilla create a mod or download this blank mod and add the events into its event folder.