You'ld need to work with someone who has a CFII as its part of the PPL and CPL training, smaller schools need you to be a CFII, have a look on web job sites especially justhelicopter (sorry heliport) they have many adds for Instructors and most require CFII, but yes its possible to work and gain hours with only a CPL and CFI, especially if the J1 visa school hires you