The pins are ordinary dressmakers/stationary pins, widely available. Some model/craft stores sell them with a plastic bead stuck to the blunt end. Like telstar says, there is not always a need to pin throught the wood.
Most hardware stores sell modellers clamps in packs of several dozen per pound. They call them "spring clothes pegs" but we know better. It is easy to reshape the ends of the wooden ones to get the grip required.