First, check the bolt and tighten it. Don't OVER tighten it or you'll cave in the notch and won't have a sqared surface to shim..
Go to an automotive machine shop and ask for some used valve shims. They're hardened steel and paper thin. Try to find some that fit over the smooth part of the kickstand's shoulder bolt. Add/subtract til the slack is gone, but the kickstand swings freely.