The 10 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. Virgil Brand purchased 5 of these.
It is unclear to me if these were truly collectors coins or not. The 10 struck may have been part of an initial run of these for inclusion in proof sets as was done in previous years, but were later excluded. The result was to keep the coins as opposed to destroy them.
The reason I speculate about this is because the dies were used earlier to strike at least 2 of these in copper as J1732/P1943. One of these ended up as part of the copper A.M. Smith set sold by Bolender in 1935. Both examples mentioned above have since been silverplated.
The 1885 Trade Dollar on the other hand was excluded from the aluminum proof sets struck that year and appears more clandestined to me.
Additional information about the 1884 dies can be found in Stack's Sprinkle sale and also in "Silver Dollars and Trade Dollars of the United States" by Dave Bowers and Mark Borckardt.
The illustrated example is the finest known, PCGS67, and was formerly in the Dunham and Floyd Starr collection.
Image courtesy of Ira & Larry Goldberg's Coins & Collectibles.