Found these bulbs today which are suitable for replacing the DRL bulbs in the 500 :-
http://www.priracing.com/product.php?xProd=374
Not cheap but I believe they are a top brand (bulb) so will see what they are like when they arrive.
http://www.priracing.com/product.php?xProd=374
Not cheap but I believe they are a top brand (bulb) so will see what they are like when they arrive.