Try this [url="http://www.instituteofbass.com/courses/music_theory_for_bass/"]http://www.instituteofbass.com/courses/music_theory_for_bass/[/url] I did it (and still doing it) a module is release every week for 12 weeks, there are not exams etc and there is a tutour available by email for questions, they also have a course forum. There is so much in the course it's unreal, they also do sight reading courses as well as technique etc.
The best bit is, it costs £19!!!!!!!