The trick with washers is the tolerances in manufacturing are insanely loose... out of the same box, you'll find some that are easily twice as thick as others. And they're often not the same thickness at one edge as at the other, and they're often not pefectly flat. So they can be a PITA.

Found some proper spacers, reasonably priced before shipping:
http://www.thethirdhand.com/index.cgi?c=Hub&sc=Spacers