The 5 coins known are believed to have come from Snowden then traded to William Woodin for returning the 2 1877 half unions and then finally parcelled out by Edgar Adams in the early 1910s. We recommend David Stone's writeup for the Eliasberg specimen in Heritage's 2019 FUN sale for more information. Virgil Brand owned at least 1 and Col Green 2.
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.