supybot-plugin-package: command not found

Have You tried accessing the binary with the full path?

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

[root@server ~]# echo $PATH

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/bin/supybot-plugin-package - from package: supybot

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