For safety, get a 3.5 or better, and 600+ on the PGRE. Lower than this is probably ok though, masters programs aren't nearly as competitive as PhD programs. A minimum is probably a 3.0 for most schools, this is sometimes a hard cutoff and it does no good to miss it.
Any of the Cal State schools, and the lesser known tech schools are all good choices. Some liberal arts colleges (I know Bryn Mawr off the top of my head) offer a masters program in physics; they don't attract top applicants so getting in should be doable.