Ideas.
First you need the Pin diameter → bushing ID (usually a loose sliding fit; common sizes are in the ⅜–⅝″ / 10–16 mm range).
Then try:
McMaster-Carr. Search “nylon spacers,” “nylon round tube,” or “UHMW polyethylene tube.” They carry many ID/OD/length combinations in Nylon 6/6 and UHMW (low-friction, wear-resistant, good for marine use).
Or
Rig-Rite. They stock a wide range of sheave bushings and stainless/nylon spacers by OD/ID/length.
You’ll want several, making sure they can rotate individually. You will not want to pack them tight nor have a single one the width of the pin.