As to the original Dixie Chicks, Kim can answer, but I figured she meant Robin, Emily, and Marty (plus possibly a 4th by the time they cut a recording). There have been at least two other transient members over the years besides those three founders.

Robin left the Chicks and now leads Big Twang, Natalie joined the sisters (Emily and Marty) and now they're on the country music charts. They're a long way--musically, economically, and geographically--from what they were originally.

As to availability of their early recordings, I'm sorry I don't know. I saw them at Winfield, where the artists brought LP's and tapes to sell after their sets. At that time they might not have produced large quantities to sell in stores.