Took my bike into the LBS for a complete tune-up and the tech at first mentioned that he thought I needed new front bearings, because there was a few mm of side to side play which he says is typical of worn bearings. After taking apart the hub, he called me back and said the bearing were fine, but that they just needed a shim to take up some of the room, but they don't have shims that small.

What is a good source of a thin shim for the front axle so I can do it myself? It's a 6800 bearing which is 19x10x5mm. I'm not sure what to look for.