The Multifactor Leadership Questionnaire assesses transformational and transactional leadership, and breaks them down into subdimensions. The scale is copyrighted and must be purchased from: mindgarden.com
An old scale that has been used in many studies is the Leader Behavior Descriptive Questionnaire (LBDQ) that assesses consideration, initiating structure and other dimensions. I believe it is free from Ohio State University: https://fisher.osu.edu/centers-partnerships/leadership/leader-behavior-description-questionnaire-lbdq
Your question is profoundly complex. There are many elements of leadership style -- ranging from the behaviors, practices, and relationships created to the underlying values and ethical perspectives of leaders.
The Leadership Practices Inventory by Kouzes and Posner has been used in hundreds of studies. Perhaps you will be best served by asking, "What precise measure of leadership style do I really want to measure?"
The attached paper may be of some value in helping you to understand some of the complexities of leadership style.
We have a project going on assessing preferred leader behaviour and personal values. We have collaborators in Iceland, Norway, Lithuania, and Russia in your region. contact me if you wish to discuss, rlittrell-at-hse.ru in Saint Petersburg, Russian Federation.
Great thanks for all replies and attached papers :). They definitely directed me on the subject and, in particular, about the differences between leadership styles. As far as I understand, MLQ is the most popular tool, but unfortunately it is not free.
First of all, you need to identify your research questions/hypotheses. This can help you identify and adopt a suitable questionnaire to answer your research questions/hypotheses. For example, are you investigating transformational-transactional behaviours, authentic behaviours, servant behaviours, ...etc?