You will need at least one LOR from a former professor. If you do not have that lined up, start now. It can take some time for us non-trad types. Beyond that, search out a manager from another division/area/team in your place of employment or past place who you know likes you and try for that even if they were not a direct supervisor. A direct supervisor is of course better if you can get one. You might try to get two old profs while you are at it. I found it easy to get one from an old engineering prof even though he didn't remember me from Adam. He asked for my old work, transcript, writing sample, resume, and then wrote me a nice one. Of course he was sympathetic, having done the non-trad LS thing himself.