US passport born in Hong Kong

Hi, I will be going to Tokyo in 3 days, planning to stay for 15 days, then flying to Hong Kong to stay 10 days, then fly back to USA. Last minute, I want to travel to ShenZhen while I'm in Hong Kong. Can I apply for a chinese visa in Tokyo? I read that if you are born in Hong Kong, you have to provide additional documents such as old passport or HKID, but I don't have any of those information because I haven't traveled for more than 20 years. Please advise. Thanks.