In the title, you refer to ATAR score, however, in the body, you're referring to study score, so I'm not exactly sure which one you're actually asking for.
Regardless, for ATAR, you receive an atar 'less than 30.' I'm not sure whether you can find the actual ATAR when you get a 'less than 30'. Maybe you do have to ask for it.
The lowest automatically reported ATAR is 30.00, with ATARs below 30.00 being reported as ‘less than 30’.
http://www.vtac.edu.au/pdf/publications/victer2014.pdf
For study score, you can get a study score of 1 in any subject, but you must've done really REALLY bad in a subject to get that.
If you complete at least two Graded Assessments, and have satisfactorily completed both unit 3 and 4, you will be awarded a study score.
http://www.vcaa.vic.edu.au/pages/faqs/vcecurrentstudents.aspx#H3N100CD
Just like like someone has to get 50?
This is a bit off topic, but is it possible to have a subject without a 50 as the highest score? Eg. Turkish and Texts and Traditions had only 48 and 49 as the highest scores in 2012. Or is it just that the students who achieved 50 choose not to have their results made public?