You can use automotive shocks on your trailer with no problem. For the shock mount, you can remove the stud that broke and replace it with one that will fit in a hole you drill where the old mount was. The new shock mounting bolt is threaded for a nut to hold it in place. You can get them at most auto parts stores that supply "Help!" brand repair parts.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.