A couple options here.  You can run a search for knife making supplies, check online auctions or make your own.  For plain brass pins, I go to the hardware store and buy brass brazing rods and just cut off the length I need for the pins.  For the fancy bullseye pins, I buy brass screws and nuts longer than I need, Put two nuts on a steel screw and chuck it in a drill, then use a bench grinder and drill to spin the nuts and round off all the edges.  Put a drop of thread loc on the brass screw near the head and twist one of the rounded nuts down to it.  After it dries, the nut will not move.  I counter sink the holes in the handles to the size of the rounded nuts.  Superglue the leftover nut in one handle and when it dries, just use a screwdriver to tighten the screw into the nut.  The I use a dremel tool to cut off the head of the screw flush. Sand it smooth and repeat for the other holes.   Sounds like another build along to me.