ConstructionRep -> Industry types (Not build constructions, the blueprint con file data)
Any Repository => something loaded from Model or Construction.con -> these are definition of something. Not an instance of some game element.
Any game element is represented by some entity (referenced by entityid) and it's component. All the entities are run by the systems, they get component data from entities to run the game.
If you have an entityid you can use api.engine.getComponent(entityId, componentTypeId)
The componentTypeId is something from api.type.ComponentType, example: api.type.ComponentType.SIM_BUILDING
There is a stockList,
api.engine.system.simEntityAtStockSystem.getStockEntities(<stockListId>, <num unknown to me>) -> list of cargo entities.
api.engine.system.simEntityAtStockSystem.getStockEntities(<stockListId>, 0) (first stock, don't ask me where to get the number)
api.engine.system.simCargoSystem.getSimCargosForSource(<stockListId>)
Otherwise try to see if you can get the info via Advanced Statistics
However, sometimes it is easier to use the old game apis, maybe the needed info is already in there.
There is api.system.stockListSystem.getCargoType2stockList2sourceAndCount too..