There is a 'Third-Way', which is an electric wiper motor conversion. They run around $150 for the motor and bracket. For an additional few bucks you can get optional delay style wipers, which run slower for mists, etc... I believe it is worth it.
If you can't find a 6v wiper moter conversion, you can get a 12 volt one and use a "6v to 12v" inverter/converter, which runs about $30 from Jim Carter and others.
On a side note, regardles of what motor moves them, upgrading to more modern wiper arms and blades for daily use has been a great thing for me. I got universal fit 10" or 11" blades from NAPA and they work very nicely.
