[jasonbvr]

Honestly mate, that would be a bit tough. With only 3 weeks I doubt you are going to want to be working anyways. There are very few short term opportunities like that available to people without a work visa. However outside of the big cities in some parts of Japan there are places where Japanese people meet with English speakers, and the English speaking people receive a "gift" for attending. However you would have to know the time and place of these types of events before going. It is not like they advertise unless they put up flyers at the location. I know of one thing that goes on every Tuesday from 7 to 9, but it would cost you about 1,500 yen to get there from Tokyo and pays only 1,000 for attending. I guess just visit coffee shops and look for flyers could be an option. Sometimes prefectural and city halls have an English club that meets once a week, but often these things do not pay since they are more of a way to meet people.