Festival sites will max out at level 5.
You will need to accumulate at least 440,000 fans and concentrate on upgrading one festival - which you choose doesn't matter - to get this done ASAP.
Showcase events, when available, give you the most fans. Other than that, I found getting 3 stars on PR stunts to be the most efficient method of gaining new fans but race wins seem to get a decent amount as well.