Can a US citizen with one entry visa in Beijing obtain an additional visa when I visit Tokyo?

Hi, Rich, it is possible. You can apply a L visa at the visa office the day you enter Japan through a travel agency. The visa office opens from 9:00 am to 12:00 am, Monday through Friday.

You need to have the following documents at hand when you go to apply:
1. A valid passport with enough blank pages;
2. One recently taken, bareheaded, full-faced photo;
3. Visa application forms:V2011A and V2011B;
4. A Chinese hotel reservation certificate and a two-way air ticket. (Or an invitation letter from China);
5. A photocopy of your Japan visa;
6. Other documents required by the officials.

Since your time in Japen is limited, I suggest you to ask for rush service to pick up your visa the next day. The total visa fee is 6,000 Yen.

Good luck!