Can I get the Jeju Island landing card and passbook in Seoul?

I can't. According to China's trip to official website. Jeju Island Landing Permit is a permit to live and work in Jeju Island. Korean visa policy, China passport holders need to apply for a Korean visa to travel to Seoul. Even if you already have landing visa in Jeju Island, you need to apply for a Korean tourist visa in China in advance before you can go to Seoul. So you can't apply for a passbook in Seoul.