I can't remember who or where I read that someone was looking for 1/4 inch mandrels. Devardi carries them. They come in a package of two rods for $3.99
you can purchase a pound of 1/4 inch stainless steel welding rod for about $13 and make your own. I either use bolt cutters or the chop saw and then grind the ends smooth.
I bought mine from a hydraulic place years ago, it was so cheap! I used a pipe cutter to cut mine. I hear of others buying brake line for cars, hobby places...
omg sorry I thought you were asking where to get some from, my bad!