How do I play on the map I want in casual mode?

[Master]

I can't find a match on train, only on dust 2. Is there any way to play on official servers on the map I want?

[Peacook]

You can't, unless if you are playing with bots, Online it is all of the players choice

[1rrat1onal]

You can play on such maps, as Train, Cobble, Mirage and etc. on official servers in casual mode only if these maps will be selected by the player's voting at the end of the game. Unfortunately, a big part of CS GO players doesn't know these maps well and, as a result, they don't select them. Nevertheless, you may try to find the map you want at the community servers list, but there is a chance you won't find it even there.