Rod Stewart’s stunning ex-wife, Rachel Hunter, went ballistic when she found out from paparazzi that the wrinkly rocker had proposed to his girlfriend, blond bombshell Penny Lancaster. Hunter is now said to be determined to get as much money as she can from the notoriously tight-fisted Scotsman in revenge. New York Post Sunday Snaps editor Jeffrey Slonim reports that Hunter heard the news from photographers camped out for her at the Dorchester hotel in London, where she’s staying while working on a new British model-search TV show. “Rod and Rachel had just agreed on an amicable settlement, but when she and their two children found out that he was getting married again, she decided to go to war. It really hurt her,” said a source. Hunter has flown to London a squad of crack lawyers headed by New York-based Mike Heller