A few questions:
Are you a gmail subscriber?
Are you using CalDav or Exchange ActiveSync?
I recently made the switch from EAS to CalDAV, CardDAV, and the gmail iOS app. In doing so, I found this:
»support.google.com/calendar/bin/ ··· r=151674
You first would have to subscribe on your google calendar, but then you go here: »www.google.com/calendar/syncsele ··· ncselect
on the safari browser and you can select which calendars you want to sync. Any public calendar I am subscribed to shows up there.
Hope that helps,