Years ago we purchased a number of iron on transfers - hexes in two sizes and grids one with 1/2 inch marks and another with 1-inch. We used them for the original battletech.
I'm pretty sure you can buy iron-on transfer sheets for ink printers and make your own. Maybe you could create a grid in a photo program, print them out, and iron them onto whatever cloth you want. Alternatively, if you know someone with a silk screen you could have them silk screen a grid on - more expensive, but would last longer.