Most people supplement First Aid with Savarese for OMT and then use subject-specific books where needed (BRS, etc.) All the medicine is the same, but the OMT is what worries most people. Some people have argued that there is no way to study specifically for the COMLEX. After taking the exam this past week, I would be inclined to agree with them.
Kaplan has COMLEX books in its course but no mass-market books are available (yet).