Rear fog lights are legal in the US- some manufacturers offer them-
I've had them on Saabs and I know they became available on the new Mini in the US after owners complained that they wanted them.

I don't think many companies offer them because Americans don't know what they are.

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Ron
Current Sports Cars:
2004 Gallardo
2004 996 GT3
1999 Viper GTS
1997 993TT
1994 965 Turbo 3.6
1978 930
1972 916
1970 914-6