cores

Hi all Trying to find out if I can just buy he valve cores rarther than buying a complete sensor and having to have it programmed back in. Any help/info would be great!!

Been suffering from a slow loss of pressure from one tyre for. No big deal. 2/3psi loss every week. No sign of a puncture. But this morning I find it very low. Out with the foot pump and it reinflates but by 1.00pm had lost 9psi. And then I had a thought. Delved around in the garage and...