A Challenge Part III: Seminoles and Southern Plains

Again, Handbook of North American Indians vol. 14, pg 451...

The Seminoles maintained cordial if sometimes strained relations with the other removed Southeast tribes and cooperated with them in matters of mutual concern. Relations with the neighboring Creek proved problematic throughout the nineteenth century, but they resolved their differences through diplomacy, often including meditation and invention by United States officials. The Seminoles also maintained cordial relations with relocated Midwestern tribes, settled to the west of them after the Civil War. The Seminoles traded with all these groups, particularly with the Plains tribes. Prior to the Civil War, the Seminoles undertook annual summer trading expeditions westward to the Great Salt Plains (north-central Oklahoma), where they traded with the Southern Plains tribes.

This may help support the family story:

In the summer of 1877... enroute to Spokane, Washington and traveled through the Billings area. He acquired this belt by trading for it with an indian who had participated in the battle [Little Big Horn].