I bought an OEM coil that was very nice about a year ago from All Classic Mustang (
http://www.allclassicmustang.com). They have many NOS and used mustang parts for many years. On the site today is listed the same coil I purchased for my 64 1/2:
Engine Coil 64 4ADB January 64, Fomoco original yellow top Mint paint & ink stamp, has mount bracket index button, Restored, $250
Try calling or emailing JD Larson who runs the site. He also is listing the correct yellow top reproduction for $125 with ink stamp.