What trim material can be used around a 6" circular permanent hole in drywall?
You could use a 6" hole saw that can be used to cut holes for recessed light cans. These can be found at any big box hardware store. After that if you wanted to trim it up you could use a 6" recessed can trim and baffle. These can be bought for under 10$ at any big box store as well. These usually attach with springs but i would think you could screw it to the drywall or even use a construction adhesive.