There are several lists of service dog providers on the internet. That's a good place to start, but remember that just because they appear on one of these lists doesn't mean they are qualified or even legitimate. It is still up to you, as the consumer, to do your research and make sure they are what they appear to be.
Service Dog Central also maintains a list of clients from our online community and the programs they've worked with so you can talk with real clients of some programs and get the inside scoop.
Resources for finding other dog trainers who might have experience with service dogs:
Certification Council for Pet Dog Trainers
National Association of Dog Obedience Instructors
Karen Pryor Academy
Association of Pet Dog Trainers
Please note that the above organizations do not screen the programs that they list. You'll have to do that for yourself. I am aware of rip-off organizations in the database, so be careful.
Get additional tips from Delta's National Service Dog Center under Consumer Information for People Considering a Service Dog.