Zekvir has a chance to spawn at higher tier delves AND upon being defeated or killing you drops some loot, this loot can contain a bountiful treasure map
So, just keep going into delves and never completing them until zekvir spawns a d kill him to have a chance at the map, repeat endlessly til you get 4 maps to get your 610 gear at the end of each bountiful delve every day
Entirely 610 geared without ever doing group content, easy game and not at all an insane thing to attempt
When you do an 8 or above you have a chance to spawn in Zekvir (The boss) Randomly. If you get him down to 20% precent health he drops a chunk of meat you can loot and it has a chance to have a map in it.
When you use a map it adds and additional chest to the delve at the end with 610 ilvl gear.