I've seen measuring devices which were marked for 16-1 ratio, 32-1 ratio 40-1 ratio and 50-1 ratio's before, but don't remember for sure where, it may have been at Walmart. If they don't have one I'd check with a lawn and garden repair service/supply house or somewhere such as a Stilh dealer. Here's one I found on ebay.
RATIO RITE GAS - OIL MIXER, 2 STROKE OIL MIXING CONTAINER 28-1111 (643370123452) | eBay