I've never owned one of the later model Coronets, but you might want to give a call to the company listed below to see if they can help you. They specialize in weatherstriping and other related parts so hopefully they can help. I've done business with them several times over the years for parts for my 1966 Coronet 500 and for my sons 1972 Dart Swinger and have been impressed with the high quality of their parts. They do sell LOTS of various parts, so I've found their web sight somewhat confusing to easily find specific parts, but if you give them a call and ask for their Mopar specialists (I believe his name is Dave if I remember correctly) they should be able to help you if they carry the parts you need.

Restoration Specialties & Supply, Inc
148 Minnow Creek Lane
Windber, PA 15963

Phone number: 814-467-9842
814-467-9842 Phone
E-mail: info@restorationspecialties.com
Website Home page link: http://www.restorationspecialties.com/