Looking for 3" Hex Game Mat

You could buy some 3" hexes and make your terrain on top of them.

You could make your own 3"hexes

you could cut up a paper map, and glue them to masonite hexes. You could also have someone make the hexes for you, and place them as needed on the board. I would use a paper map, and add terrain tiles to it. You can move them around, still have an actuate LOS measurement without all of the mess, and questionable measurements. Just a thought

  Thanks Dano;
 
  You do raise some good points regarding mess & questionable measurements.
 The measurement issue is one I am actually wrestling with finding a solution for.

 The goal of making my mats is to have something that looks as life like as possible. Which would mean if I used individual hexes I would need a fair amount. This is one of the reasons I went with the 1" foam. I wanted to be able to sink my rivers and lakes down into the foam. Then I will make hills & forests to go on top. (Typically to cover 2 - 3 hexes at once.)

 I attempted to draw the hexes on the top using a template I made and it was a disaster. My hexes went out of square and would not line when I added a second board.
I looked into getting a 3' X 3' stencil made and that was going to be cost prohibitive.
  

I wrote this up a few years back - maybe it can help you

kahlich.wordpress.com/2013/08/26/how-to-make-hexagon-maps-for-axis-allies-miniatures/

www.youtube.com/watch?v=SxhJM-VlhO0