Well, the only places I know that are good to train at are the Sports Domes in Nimbasa.
There should be Level 60s or so there. If you're lucky, you may come across a Doctor who has a Level 65 Audino. I would recommend having Exp Power ++ on at that point with Lucky Egg attached, seeing as you can get a total of around 28,000 Exp from that.
Sorry, it's the only place I know of...