I finally got around to implementing the MacPaint file format, so now you can not only convert all your old MacPaint files to PNG, but also the reverse.
If you rescue any old MacPaint files please send them to me for archiving on macpaint.org!
GitHub - thejoelpatrol/macpaint_file: Convert MacPaint PNTG files to modern image formats
Convert MacPaint PNTG files to modern image formats - thejoelpatrol/macpaint_file
GitHub (github.com)