rpmrebuild: 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
/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/bin/rpmrebuild - from package: rpmrebuild

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