It's definitely lawn mower season and we know what the supply stores and repair shops charge!
I have a couple dozen or so different types of Mufflers from large tractor ones to push mower, mini bike Go cart type. Check the pictures out. See if it looks like what you need.
Some of the larger ones come with the mounting hardware.
These are New Old Stock.
I also have a half dozen or so of Tecumseh needle / seat kits. The Numbers on the package you'll have to cross reference it to your own needs.