Only the default calendar is sync-ed when you setup your google account on your Windows 8 machine for the first time.

Using Chrome browser as reference,
1. Download [User Agent Switcher] from the Chrome Webstore
2. Select an iOS device
3. Go to ''
4. Select [Settings], [Show advanced settings], [Content settings]
5. Deactivate Javascript by selecting [Do not allow any site to run JavaScript]
6. Click on [WindowsMail]
7. In the URL, change 'supportMultipleCalendars=false' to 'supportMultipleCalendars=true'
8. Submit URL (Press Enter)
9. Enable the additional calendars and save the settings
10. Readd your Google Account to your Windows Calendar app.