Fairly sure that all brands make racing shoes in smaller sizes,its simply a case of whether the retailers buy them to stcok in-store.As "Ace" says,Start Fitness have a fair number of smaller racing flats (3.5,4,4.5 etc.) as do Sportsshoes Unlimited.
As Annajo says,dont just go for Adidas on the advice of one physio,go with what feels comfy for you.