I will assume that since you asked this basic question, you are not very experienced in knifemaking. All of the knife supply catalogs sell pin and rivet stock by the foot. Try Jantz, K&G, Texas Knife Supply, Pop's, or Sheffield. Local hobby shops, and many hardware stores, have a small rack of brass, nickle silver, and stainless rod and tube for hobby work.
More of an important issue is your choice of handle material.
Carbon fiber is nasty stuff - if you don't respect it.
It is an irritant to skin, eyes, and lungs. You need a good filtrate mask, eye protection, and long sleeves. The dust needs to be vacuumed up from the work area -and off of you - before leaving the work area. Don't work CF in any living or cooking area (bedroom or kitchen). To be honest, you should only work it with a dust removal system. definitely not a starter material. I would get some stabilized wood or Micarta.
With any handle material, wear a filter mask when sanding and clean up the dust.
Stacy