The worst time to go looking for a doctor is when you need one. It's always best to have an ongoing relationship with a local doctor. Good medical care is as much about preventing illness as it is about treating it & that requires careful surveillance over time, usually coordinated by a general practitioner (GP).
Think of your doctor as the conductor of the medical orchestra. The GP's job is to keep you 'in tune', by coordinating their skills with those of the rest of the orchestra - the specialists (pathologists, radiologists, surgeons & the like).