I've used various fabrics to filter my butter . . . . no harm done.
next time you can't find something just look for a colorless sheet of some sort that you can cut a chunk out of, make sure this sheet doesn't have lots of fibers coming off it like hairs and such.
I use one that doesn't get anything into the butter whatsoever . . . . after you find one that works it's best to just use it over and over. just clean it real good with hot water every time.