Well, I know there is a trainer with a Swalot somewhere, but you have to rematch them a couple times. Or you could catch a Gulpin on Route 110 and get it up to level 26 to evolve. For Heracross, no trainers have them, but you can find them in the Safari Zone. After you get an Acro Bike handy, go into the Safari Zone and go north. You'll see the Acro Bike tracks, and then traverse it. After you reach that area go into a grassy patch and hold B. You'll bounce in the grass while finding Pokemon without wasting steps. Note that Heracross are kinda rare, so you need patience. You can also find Phanpy in that area.
Hope I helped!