There is a (pretty hard to find) option to only use local materials in the stations, but I can’t find the same in stockpiles. I created a stockpile next to my seat fitting station, and it immediately bought a new set of seats from the outside, even though I build my own. Even later, when new seats were removed, it would rather buy new seats than get the ones from my own “make seat” station
I believe Cliff has mentioned this may be something to be added down the road. But I’ve noticed the same, and tried to build the stockpiles between the place I make the items, and the production line, and not letting them reach an outside import place. Unfortunately, it only works with some stations, Seats will not, as you need to bring in outside heaters and Leather, and that will require an import station. So the Stockpile still pulls from the outside.
He said he wanted to fix this here: