zblacklist: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/zblacklist - from package: zmap

You may install the required package with command yum install {package}

Error in other languages:
zblacklist: bevel nie gevind nie
zblacklist: comandă negăsită
zblacklist: comando não encontrado
zblacklist: commande introuvable
zblacklist: command not found
zblacklist: käsku ei ole
zblacklist: không tìm thấy lệnh
zblacklist: komanda nerasta
zblacklist: Kommando nicht gefunden.
zblacklist: kommandot finns inte
zblacklist: komut yok
zblacklist: nie znaleziono polecenia
zblacklist: níor aimsíodh an t-ordú
zblacklist: no se encontró la orden
zblacklist: no s'ha trobat l'ordre
zblacklist: opdracht niet gevonden
zblacklist: parancs nem található
zblacklist: perintah tidak ditemukan
zblacklist: príkaz nenájdený
zblacklist: příkaz nenalezen
zblacklist: команда не найдена
zblacklist: командата не е открита
zblacklist: 命令找不到
zblacklist: コマンドが見つかりません