Available as a single model #9015 from 1984-1988 in Palomino, Buckskin and Bay. Variations include one back right sock or all four socks. The four sock variation is seen in the 1988 catalog. Early packaging has a copyright of 1983, but was listed as new in the 1984 catalog.
The Bitsy Breyer Western Set #1015 included Bitsy Breyer doll, Western Tack, and comb from 1984-1987, in Palomino, Buckskin and Bay.
Side note: Models released in the 1987/1988 timeframe have been known to shrink.