I am specifically trying to locate this instrument for my current research using Attachment Theory. I need to find out more about its reliability and validity. Any assistance in providing me with leads is greatly appreciated.
As Hendrika mentioned, you can find it online. However, you might want to take a look at these two papers that review such measures. Most older measures are quite flawed, particularly if they were not developed using item response theory (IRT) analyses. I have been working on improving assessment in mental health areas, and it is amazing how bad some of the 'gold standard' measures are. Here are two good articles on this:
Pilkonis, P. A., Kim, Y., Yu, L., & Morse, J. Q. (2014). Adult attachment ratings (AAR): An item response theory analysis. Journal of Personality Assessment, 96(4), 417-425. doi: 10.1080/00223891.2013.832261
Fraley, R. C., Waller, N. G., & Brennan, K. A. (2000). An item response theory analysis of self-report measures of adult attachment. Journal of Personality and Social Psychology, 78(2), 350-364.