Yeah, it should be under the tune shop @ honda under full models.
I'm currently collecting all the cars and only have about 15 more to pick up. Unfortunately they total to 32,900,000 Cr. I've been DTMing alllll day long...
Theres a number of cars hidden like that. Off the top of my head, they'll all Japanese, they all have the tune shop name in the name of the car, and they are Honda (Mugen), Nissan (Nismo), and Toyota (TRD). No Mitsus or Mazdas from what I remember.