I'm sure one could be built, but I think I'd start with a visit to Tractor Supply or a similar store and se what's already out there. Unlikely that you would find a bolt-on, but there are lot's of small mufflers out there for the smaller engines often found on tractors. Building a muffler from scratch is a tougher proposition than you would think. I looked into it once and decided that finding one made a lot more sense. I actually found a place in England that would make what I wanted and, since several were needed,that has worked out great.