A few months ago I picked up a '82 Suzuki GS850 cheap & decided to sell it to make some cash to fix my CB550. Before I sold it I snagged the mirror cushions (that's what they are called in the parts manual) part # is 56700-31001- they go for under $12 each & are still available from the dealer. I didn't think they would do anything to stop the mirrors from vibrating, the mirrors seem almost loose & floppy, but I was really surprised, they actually work! I'm running clubman bars & they raise the mirrors up & out about an inch, for the first time I can see behind me clearly, not just a blurry image of my shoulders even at highway speeds.
Part #4 in the diagram: