I would imagine it's hard to find job postings because, since it's not as physically demanding as hospital work, people tend to stay in those positions until older ages. However it can never hurt to walk in with your resume and ask to speak to the person in charge of hiring. You can also call and ask if they are hiring RN's, but walking in is probably better.
I like my hospital job too much to consider leaving right now. But in 5 or 6 years, once my kids start school, I'll definitely be considering a doctor's office or outpatient job so my hours can be more compatible with school hours.
OP, have you considered outpatient clinics as well? Most major hospitals, especially children's hospitals have several outpatient clinics that my be more accessible than a doctor's office. My current hospital has outpatient clinics for: Allergies and Immunology, Pediatric sedation, Cardiology, GI, ENT, Endocrinology, Hemophilia, Sickle Cell, Pulmonology, Neurology and an oncology center for kids to get chemo on an outpatient basis.