There is an element of luck/randomness to getting rematches, but I've found that walking around a lot on the same route as the trainer helps trigger rematches.
If you just want to Sketch a move, you could fight Gabby & Ty, since they're always a Double Battle and you don't have to wait for a rematch like with other trainers.
haha, i must be really tired i have no idea how i completely forgot about gabby and ty