Concerning the kibbles that you have tried:
Did you keep the dog on 1 kibble, (no other treats) for at least 8 to 10 weeks before switching?
A dog could possibly itch even MORE if it is "detoxing" from whatever ingredient it was sensitive to in a particular food. So enough time must be allowed for an "elimination diet" to work properly.
And, as mentioned, you could be seeing environmental sensitivities.
*New dog bed
*New carpet, flooring or furniture in the house
*Change in laundry detergent
*Chemical lawn treatments
*Or just trees, grass, bushes, flowers, etc.
The list could go on and on!
Best of luck to finding the right food!