To be accepted in any masters program, you're going to need at least one professor that will look at your application and say "yes, I'd like to supervise this student".
Normally, the admissions committee would be inspired by letters of recommendation from your undergrad profs, but in your case you'd be better off with letters from your current employer saying how dedicated and hard working you are.
Have you published any blogs etc. that demonstrate how well you can write? Do some of them discuss specific topics in history, showing your interest in the subject, and your knowledge and ability to analyze the facts and study their relationships?
But if you are able, the most helpful thing would be to visit the university and sit in on some classes. You might find it so boring that you'll change your mind. Or, you might find it so interesting that you'll discuss things with the professor. If you can impress a prof or two, that's where your most effective letters of recommendation will come from.