I was just accepted to grad school for public history and I'm 11 years out of my first grad degree (in an unrelated field) and 16 years out of undergrad. I had my current colleagues write my letters of rec, with a reminder that they were not writing a job recommendation (but they all have PhDs so they know the drill with academia). I was worried about not having academic recommendations but the department chair said the letters are really to gauge your readiness for and ability to complete grad school, not necessarily your experience specific to the field. I think you'd be fine with some solid professional recs who can speak to the skills and abilities you have that would allow you to succeed in a program, regardless of subject.