The 5 coins known are believed to have come from either Idler or Snowden and were parcelled out by John Haseltine and Stephen Nagy in the early 1900s.
They are believed to have been deliberately struck for sale to collectors. Unlike the 1884 trade dollar, examples were not included as part of the aluminum proof sets struck that year.
Additional information can be found in "Silver Dollars and Trade Dollars of the United States" by Dave Bowers and Mark Borckardt.
The illustrated piece is the Eliasberg coin. Photo courtesy of J. Parrino's The Mint LLP.