I did ask around for you and did not receive feedback. Sorry. I could try again. I feel like I asked then they promptly came down with pneumonia. How close are you to Chester County?
The certification thing, I would be flexible on. Behaviorists, yes. Trainers, maybe. I'd be interested in their continuing education (what seminars, training "camps", Clicker Expo, etc.?). Length of experience depends on the person. There are some exceptional younger trainers (Hannah Brannigan and Sarah Stremming come to mind). I find there are a lot of fixed mindsets in the dog training world and a person whose been using the same methods since 1985 and claims that if it's not broke, why fix it might not be on the same page as you. I'd ask them who their favorite trainers are. Jean Donaldson, Patricia McConnell, Susan Clothier and Bob Bailey should be on their list. Instead of looking for a spaniel specific trainer, you might broaden that up to sporting dogs.
Might be worth reaching out to your local obedience club, breed club and your breeder for suggestions, if you haven't already.