From what I have heard of working broadway, you are best off getting yourself an agent (yes, agents are not just for actors). There are some which deal with stage managers (and other positions), and it takes a lot of the stress out of the job. I am not talking your "hollywood star" type one on one agent, but rather one of the ones where you meet them a few times, give them your resume then 2 weeks later out of the blue get a call "Be at x and y at 2:30 for an interview to work on ______". I temped in one between shows for 2 months and a lot of unadvertised positions were made available at the agency, some companies for example, worked exclusively through them.
However, that said, before you jump in the deep end, do you have a good professional grounding? By many, broadway is considered the pinacle of positions to hold - even some AU SM's aspire to work on broadway in the US or UK.