Both Pokemon Trainer and Lucas are in the stage where you first play as King Dedede, Ness, and Luigi. Lucas is in plain sight along the main path, the only reason you wouldn't have found him is you weren't focusing on character trophies at that point (I certainly get nervous inside Subspace, so I understand). Pokemon trainer is a tad out of the way. In the room with lots of vanishing stairs, there is a floor with a block wall, a spring, and a large "ball" enemy. Jump on the spring and hit the bomb block in the wall. You will see a door.
Through the door you will immediately see Pokemon Trainer, but you might as well get Pikachu here to. To get Pikachu, hit the bomb block, dash in and grab Pikachu, then run like nobody else has run before back to the door because the floor starts to vanish as soon as you blast the bomb block.
