Other bike sites that I frequent have a list of members that hold parts like shims or specialty tools as a "sticky"Locally it's contingent upon being friendly with a workshop mechanic, or knowing someone who has a bunch of spares.
Here I'll start
I have
8mm Ducati shims
29mm Kawi shims
29.5mm Suzuki shims
OEM shims usually are better quality and offered in more sizes