Yes, it is a problem finding clinicians with interest in and experience with ADHD adults. In larger cities there are usually a handful of people who qualify, sometimes associated with teaching hospitals. Another possibility is asking at a college or university health clinic (even if you don't attend there).

Organizations like CHADD, local or state psychiatric associations have referral lists that can be useful. Likewise some insurers publish lists of clinical specialists. Other folks with ADHD who are in treatment might have a practitioner with room to see a new patient.

Pays to keep trying to find a provider you can work with, it will happen sooner or later and will be well worth all the trouble you went to.