For whats its worth, I found a supplier for wood in the Chicago area.  It is Door and Plywood Co at #708-599-0200.  His name is John.  He does have a $150 minimum order which he said he could give me three sheets of Okuome for.  He also deals with Meranti and Sapele.  There is also Wood World in Chicago which is more expensive, but local as well.  One other company worth mentioning is The WorkBench in South Bend IN at #574-277-8350.  I probably called over 30 plywood suppliers and they all thought I was nuts asking for 1/8 or 4mm ply.  Not only is it impossible to find the 4mm, then you have to make it marine grade.  You would think it would be a lot easier to find. Don't we live next to some lake....?  Good Luck!