How could I find out if a previous employer is slandering me to new employers?

I have a big issue here. I was terminated from my job about six months ago after wokring there almost nine years. I had got into an arguement with another coworker, which was a friend of mine up to that point, and the so called friend said I shoved her into the wall. Well the union fought for me and I lost. I havent been able to get a job since then and I have it in the back of my mind that the Human Resorces woman is probably saying some bad stuff about me. I was always a good worker and at one time was #1 where I worked but when new management came into the picture, and I changed from working production to being a material handler, I didnt seem as important to them and they always gave me a hard time. The HR lady always looked me up and down like I was a bad person and actually told some of my friends not to talk to me because I like to start things. I know that they cant slander me if a new possible employer calls them but if in fact they are, how would I know?