There are no catalytic converters on any Deere lawn and garden equipment. Not that that has anything to do with leaded/unleaded vs. ethanol-free....
And? I can go find lots of parts that fit my truck but aren't on my truck. Both of the mufflers you found are aftermarket items being advertised by the OEMs, not by Kawasaki or Deere. I'd think that if Kawasaki was building their engines with a catalytic muffler then there wouldn't be much of a market for aftermarket suppliers. Those two company's ads you found are trying to sell their mufflers to companies like Deere. The Deere manual for the machine makes no mention of any catalytic muffler. The Kawasaki manual for the engine makes no mention of one either.I looked online and saw that the same Kawasaki Engine in my S240 might have a Catalytic Converter. I found this part pictured below.
Note that there is a $100 markup on ALL CARB compliant Deere mowers. That applies to the S100 series, the S200 series, the Zero turns, etc... It isn't unique to the S240. None of the others have catalytic mufflers either.The JD Dealer said that there was an additional $100 charge for required California emissions equipment. Might that include a Catalytic converter in the muffler?