FWIW, I had my wife bring me some from the States but the ones she bought aren't hefty enough. They have cracked and are a pain to get the post secured without the shims rotating a little, so sometimes I've ended up with cockeye'd speakers. Once I have those speakers on poles I am loathe to pull 'em off and reposition the shims.
Mine are nylon shims. I can see where wood or plastic would crack, but these are pretty much indestructible. Plus they are exactly the width of the tongue on the tilter, so easy to keep aligned.
