Assign a Pokemon with the Crush specialty to produce Limestone passively. You'll still find it while exploring, but the helper output adds up. It goes into 1 recipe, so having a passive supply helps.

A sedimentary rock used for marble

Raw Material
MoveRock Smash / Caves
Rock Smash Crush specialty Caves
SteelixCrushCranidosCrushLarvitarCrushGolemCrushGravelerCrushPawmotCrushTyranitarCrushBastiodonCrush
Limestone→ConcreteConcrete Mixer

Concrete is used in 7 crafting recipes

Concrete goes into Asphalt Road, Concrete Pipe and 5 more. Most fall under Blocks and Utility with 2 other categories — use the filters below to narrow it down.

7 recipes
Asphalt RoadBlocks
Concretex2
Concrete PipeOutdoor
Concretex2
Concrete StepsBuilding
Concretex2
Concrete WallBlocks
Concretex2
Elevator PlatformUtility
Glassx8›Concretex8Tinkagearx2›
Lift PlatformUtility
Iron Ingotx5›Concretex5Tinkagearx1›
Warning WallBlocks
Concretex1Iron Ingotx1›

There are 1 recipes that call for Limestone, and 1 of those are Blocks items. Scroll through or filter by category to find what you're looking for.

1 recipe
MarbleBlocks
Limestonex4