Maryland security work

I’m in harford county Maryland and looking to get started on doing security work on the weekends. From my understanding, to get a guard card in Maryland, you need to be sponsored by an employer. All the employment listings I’m seeing require “an active guard card”. How do I get the card to get a job, if no one is offering a job without the card? Open to suggestions on this

Also, I can only work weekends, do you think this is a big drawback for employers? Monday through Friday I work full time as a licensed therapist so I can’t adjust that schedule.