Unfortunately there really isn't a substitute in this case. If you want to make chili oil you should track down the correct chiles. Online ordering makes it so easy. In a pinch Korean chili flakes are definitely better than the Italian style (cayenne) chili flakes you're used to seeing in American spice aisles. Remember, the only reason to make homemade Sichuan chili oil is to do it right. You want that unique flavor!