To get the 12 policies you will need a mix of government, leaders, wonders and great people.
These are what I found.
Government needed - Democracy = 8 policies
Leader - Pericles (Greece) = +1 Wildcard slot
Great Person - Adam Smith (Merchant) = +1 economic slot
Wonders - Forbidden Palace = +1 Diplomacy slot
- Potola Palace = +1 Wildcard slot
- Allhambra = +1 Military slot
- Big Ben = +1 Economic slot