Maybe you could take a look at the Turnover Intention Scale (TIS-6). I haven't been able to figure out if the questionnaire is reliable, but I'm sure research has the answer for you.
1. I often think about quitting this organization.
2. I intend to search for a position with another employer in the next year.
Source: Bentein, K., Vandenberg, R., Vandenberghe, C., & Stinglhamber, F. (2005). The role of change in the relationship between commitment and turnover: A latent growth modeling approach. Journal of Applied Psychology, 90, 468-482. Adapted from Hom and Griffith (1991).