I am so sorry to hear about the issues you are having with your bulldog. Have you tried changing your dog's diet? Can you please let us know which brands you have tried and the types of food (kibble, canned, raw)?
Have you tried a raw or freeze-dried raw food diet? It can clear up an enormous amount of issues, as I found out when I put both of my 15 year old dogs on a freeze-dried diet.
Finally, I am sure there is a vet out there that will know what kind of diet works well to prevent cystine bladder stones in dogs. If you do a web search, you may be able to find a specialist in the field who will do a phone consult. Vets prescribe a very specific diet for cats with bladder stones all the time so I am sure it is the same for dogs. Diet is often key in my opinion.