is there anywhere to buy them other than the dealers?
Do mud flaps help keep the dirt off ?
Can i buy wind deflectors anywhere?
Sometimes the mudflaps and wind deflectors work out about the same price as the dealer by the time you add postage, sometimes a bit cheaper. If they are a lot cheaper may not be good quality.
Ebay is probably your best bet, just make sure you double check the series and model (for example I think the wagon variants of both the FD and GD i30's use different rear mudflaps and wind deflectors than the hatch)