I used to use steel shim stock that came in .001\" sheets for industrial alignments ... might be easier than machining (easy to cut to shape), and more \"crinkle free\" than aluminum foil. A quick look at Grainger shows it in .001, .002, .003, .005 and .010 for under $20 and 316 stainless @ .002\" +/- .0001\" for $35 ish. Other sources/sizes abound as well.
