Just put "brown letters" in the FABO search box. You'll have so many hits! I've had so many BFGs with the letters turning brown, I'm afraid to take the blue off of these 2 year old ones. Yet the older ones on my 70 Dart are just fine, but too old to safely drive on.
65 Dart fronts, 2 years old...
Do you have a picture? This is mine on my 1970 Dart 340 Swinger (sorry not for sale). Your description sounds like mine. You may be limiting your search. Good luck! Rick