If you can't find any original Honda or similar sized non-Honda blades, go to a well-stocked hardware store and buy yourself a quality steel Brush cutter blade, flat type, 14 or 16 inches long. There's a few Japanese ones on the Thai market that last long(-er) and will cost you around 300 Thb.
Have a metal shop cut, drill, sharpen and reshape that into the blades you need, maybe an extra pair for later. Thickness should be okay; none of my blades is more than 2 mm.