I see that some trainers have lv. 60 or so pokemon. How do I get those with the vs. Seeker in Platinum?

I was looking at trainer rematches and some have lv. 60 pokemon. What event do I need to do so that the trainers have lv. 60 pokemon? (this is in platinum). I use the vs. seeker and one hiker has 2 steelix but the guide says he has camerupt and donphan and steelix. help!