Their are quite a few hypoallergenic pet foods out there it is just finding one that is suitable for your dog!!
James Wellbeloved
Nutro
Wafcol
Burns
Skinners
Arden Grange
all do a food that is available from a good online petstore
Hypoallergenic Dog Food UK
all ranging in price but read through and it is going to be a case of what suits your dog, what are you feeding at the present!!!