Bosch Motorsport has an aftermarket ABS system (http://www.bosch-motorsport.de/en/de/ueber_uns/leistungsangebot/systemkompetenz/absm4paket/absm4paket_1.html) and I believe Turner Motorsports does too. They are both VERY expensive and the installation is far from simple. Even Bosch Motorsport admits, ABS provides minimal benefit on dry pavement. My advice would be, keep your money and don't drive in the rain!
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