I don't know, what files you are looking from ftp, sorry.
There are two ways add maps in CS:GO, old way
and workshop maps
-For upload missing map to players, old way
upload file from srcds server or from sv_downloadurl address.
maps are uploaded from Steam web site.
You see "de_castle" in vote because it is installed in your game, you have played that map someone else server or you have pic it up from steam workshop.
So, lets stick first on workshop maps. Those maps maybe be problem to handle on later because it have "workshop/id/mapname.bsp
What you need to do is set Steam API -key
in your server.
- In server, create txt file into csgo folder: webapi_authkey.txt
- Go wep page and sign in with your own steam profile: https://steamcommunity.com/dev/apikey
Register Steam Web API key, give simple domain name what ever you like.
- Copy paste key
part only into your server ...csgo/webapi_authkey.txt
Browse -> cs:go maps from workshop
When you look one of maps, check url address. It have map ID number.
- Copy that ID number, add it in server file ...csgo/subscribed_file_ids.txt
- Reboot server. The download could take some time, minutes. Wait. You can also see console messages when workshop map is downloaded.
After this, change map to else and look maps list: maps *
If you can't see any workshop maps in list, reboot server. And try again look maps *.
To load map: changelevel de_castle