vintage car stereo question

[L72copocamaro]

I've bought a lot of stuff from Crutchfield over the years. They provide install kits with the equipment they sell. Might be a long shot, but maybe they have some vintage kits still. Or you might try some local installers. I installed many stereos and always kept left over parts because it might come in handy. You might get lucky with one of them. Other than that, maybe try some swap meets and garage sales.