My mistake LGW Vulture, sorry
But you will see ACJ mostly in Europe. I think that Privajet or Comlux Aviation Maklta are the best options. I think I saw information couple weeks ago that Comlux Aviation is hiring for their ACJ`s, but I don`t know is it still available.
Anyway, I think it`s much harder to get job on ACJ than on BBJ. Maybe because there are not so many of them.
There is also one ACJ operated by China Sonangol International reg. VP-BEY
Also one operated by National Air Services at Jeddah, KSA reg. VP-CKS
Look also at System Capital Management at Kiev, Ukraine reg. P4-RLA
Volkswagen Air Services operates two ACJ`s I think, maybe you should find some information about them, but I`am sure that you have to be fluent in Germany if you want to fly for them.
Anyway, sorry for my previous mistakes and I wish you luck!