Howdy Tin,
I just made the switch from vulcanized fiber spacers to G10 myself, so the link is fresh in my mind.
I got sick and tired of putting a perfect finish on a knife and coming back the next morning to spacers that had expanded or contracted relative to the humidity level.
Go to
http://www.alphaknifesupply.com/micarta.htm
Chuck's a great guy and has G10 as thin as .004" available.
Hope this helps,
Taylor