They are called jack posts kits by CPC, part numbers CN06422 and CN06421 for starters. You might get a better price for the quantities you require elsewhere. £0.90 for a pack of 5 of the CN06421 + vat looks ok to me.
You need to make sure you get the right thread; while the vast majority are 4-40UNC ones with M3 threads also exist. I use a lot of the 4-40UNC variety in products and they're a right PITA, especially in brass. When tightening them up just another little tweak feels like it should be fine, except that it isn't and the core of the screw fractures.