At what level are you looking for the organization? Many experience the organization in relation to their experience with their direct manager. This, 2 people in the same organization can experience trust quite differently. I wonder if you used OCB and LMX instruments as proxy measures.
I believe you may benefit from the following article:
T.K.Das and Bing-Sheng Teng (1998) Between Trust and Control: Developing Confidence in Partner Cooperation in Alliances, Academy of Management Review, Vol. 23, No. 3
This article discusses the nature of trust, development of trust due to cognitive and affective factors, behaviors due to varying trust levels, and implications on performance. The author has developed a scale which has since been used by researchers to explore trust within teams, trust among senior team members in organizations, trust between functions within an organization, and trust between professionals dealing with an organization. You may find it suitable for your study:
McAllister, D. (1995). Affect- and Cognition-Based Trust as Foundations for Interpersonal Cooperation in Organizations. The Academy of Management Journal, 38(1), 24-59.
Very interesting question indeed. Above and beyond the suggested wonderful articles, I think that the very same elements that help construct/build trust (i.e. organizational transparency) could help measure it provided that the relationship of cause and effects between transparency and trust is scientifically demonstrated.
I think that the following review is what you are looking for to make up your mind on what suits your case best. I'm researching tust at the moment as a multilevel construct and it has helped me significantly:
Dietz, G. and Den Hartog, D. (2006) Measuring trust inside organisations. Personnel Review. 35(5), 557-588
It reviews 12 assessments of trust based on the specific set of dimensions they research (you can see them all in the appendices). The rationale and the literature review on the matter is excellent. I believe it will give you all the insights you need for your research project.
I have written several papers -- and a dissertation -- about organizational level trustworthiness. Attached is my c.v. Perhaps the instrument I developed will help you.