I usually remove the core with my fingers. Pliers work for the ladies.
Bike shops do not carry spare parts and when you go there to buy something, they will try to convince you to buy something else (what they have on hand that clearly does not meet your needs) or maybe offer to order. I understand that they lack capital, why else are they so beholden to Specialized and Trek. Why bother going there?
Every bike shop on the planet? Well, the one I am in does carry spare parts, but occasionally (with over 40,000 items skewed) we need to order something.
But we do fix home repairs.