Loot a Treasure Hunter, after you took the treasure map disconnect the internet.
He will spawn again every time you load in. Works with legendary animals too.
One of the perks of pre-ordering Red Dead Redemption 2 is that you get a digital treasure map that shows the locations of "secret buried treasure" throughout the world. If you're interested in this perk, you have to pre-order soon. Rockstar is only giving out the treasure map to those who...