Bahco makes a 36" bow saw, with two types of Bahco blades available: for green wood (with some raker teeth), and for dry wood (with simple "peg" teeth). I have one and I like the longer stroke on the bigger trees. I also swap blades depending on what I'm cutting (green/dry, hardwood/softwood),
Even more heavy-duty than the Bahco is a 30" Swedish military surplus bowsaw, which are built tough and should come with an unused blade; the blades on mine were new old stock of excellent quality, made in Sweden. Even though they were the "peg" type teeth, they cut very well even in green wood. Another good thing about this 30" saw is that it had a similar distance between blade and frame as the Bahco 36" saw, which affects how big a log you can cut. The smaller saws typically have a smaller distance.
The Swedish military bowsaws can be found online from several sources, and the price range goes as low as $5 each plus shipping, which is a true bargain.