I wouldn't be too worried about finding a specific brand/model muffler. I tried researching them as well recently but glad I didnt bother in the end.
Just grab any generic 3" oval muffler with centre/offset layout, can get them cheap off eBay.
Here's my mid-section i knocked together a couple weeks ago. Thought it'd be too loud considering the size differencec but it sounds awesome, perfect amount of growl and barely noticeable at highway cruising.