There is a service out here in Los Angeles, that can create a food formula for you that will be tailored for your pup's needs. All food formulas are created by a team of vets. The questionnaire alone took me an hour to complete and they still wanted all vet records, and possibly wanted to speak to all vets my pup has seen in the last year (regular vet, and his current specialist). My pup's neurologist team has highly recommended them to me. They also have pre-made, or can make your custom formula for you. Seeing as how you're not in our area, the recipe they create for you can be made at home.
https://www.justfoodfordogs.com/
I'm sure there are also other similar services in your area. We currently opted out of this service, as my pup is having other health issues. Once his current health issues as addressed, then I will be signing up for a custom formula with them.