So the general rule is that, if you make contributions to political
parties, you can claim a tax credit (line 25 form A) of 30% of the
contributions (less 10,000 yen) up to a maximum of 25% of your
previous year's tax. There are complications if you also make
donations to qualified nonprofit organizations, but according to the
guy at the tax office, there are no special restrictions for
foreigners. That said, he was only speaking from a tax perspective.
There may be limitations imposed by other regulations.

Tim