If you have admin permissions (or in singleplayer go to "open lan game" with "enabled cheats", you can use the command:
/give @p filled_map{map:#}
So e.g. if you lost the map with the number 20, type
/give @p minecraft:filled_map{map:20} 1
If you don't know the number of the map, go to you world-folder and take a look into the data
directory, there will be files named e.g. map_20.dat
.
Every file you see there was/is one map that somebody created on you map.
So you just need to try all existing numbers until you get the correct map.
For the future I would advise you: Always make a copy of important maps and keep in a safe place.
When one of the maps gets lost, you will see, that the map-copy will always have the same state like the "original" map (because the data of all maps with the same ID is stored in the same file in you savegame)
EDIT:
@Michael asked how the command for bedrock would be.
Unfortunally I can`t test it on bedrock, but according the minecraft wiki article about the give command, the syntax for bedrock is minimal different like this:
According this example I thing the correct bedrock syntax to get a filled map should be:
/give @p minecraft:filled_map 1 0 {map:20}