My family physician misdiagnosed my mother as schizophrenic, but we know she has dementia. Where can I find an experienced doctor in geriatric medicine?

Unfortunately, geriatricians can be hard to find in some communites. If your local clinics can't provide one, then try a neurologist who can do brain scans and other tests for dementia. A psychiatrist (a second one if the doctor you mention is one) can do these tests too. Ask ahead if they work with elders who may have dementia.
Carol