Hi Vm,
A few Options below. I haven't seen them for sale online.
Find an old free mower for parts.
Ask in a mower shop.
Use steel Cup washers instead.
Machine some up on a Lathe.
3D print them.
The "Community" Route (Cheapest)
Many local libraries or community "Makerspaces" have 3D printers. Since a washer takes very little time to print.
Cost: Usually $2.00 – $7.00.
How it works: Libraries often charge a small flat "setup fee" (around $5) plus a tiny amount per gram of plastic or hour of print time.
Wait time: Often 1–5 days depending on their queue.
