but for now, all the methods of cobble generation won't fit nicely on my wall, so I just spawned scrap for these tests.
If you've got Thermal Expansion, use Igneous Extruders, just one block. They need one bucket of lava and one of water to start but don't use them up and automatically pipe out cobble to a side of your choice. It's only one every two seconds but you can build as many as you need.