A Master's program, unless it's an SMP, will not help your grades. Any prereqs you got less than a C in you should retake and you have to ace them. Nothing less than an A-. You can do these classes at your local college/university. I wouldn't do them at a CC since you're retaking and trying to show adcoms that you can do well. In your situation, it'll look like a cop out if you do them at a CC. You don't necessarily need to register with a formal post-bacc program, you can DIY it.
If all of your prereqs are C's/C+'s, then maybe retake a couple of those and then take upper level courses in those prereq categories to show that you can do the work.