I would recommend hiring a barefoot trimmer instead of a farrier. Some farriers are open minded enough to give it a try, but just lack the training and it's really hard for them to resist a little sole paring here and there or don't bevel the walls enough. It's easy for them to resort to shoeing instead of working through any glitches, as well. They just sort of think differently. If your horses are already without shoes, the trim can only make them feel better. No transition period to worry about, so it will be super easy for you.
When hiring either a trimmer or farrier, ask them what experience (how long, where) they have. Where did they get their training? Are they certified?( Being certified can sometimes not mean much, unfortunately, and I've seen some talented ones that never went to school for it.) However, it's a rare person that can just pick up some nippers and do a quality job. If the training didn't come from a reputable school, there should be some hands on training from another farrier/trainer (apprentice) . I don't mean casual "training" where they watched their farrier once, either. A clinic here and there is helpful, but there should be some consistent guidance in there. Either way, they should be honest about their experience, or lack thereof.
I personally think the best barefoot trimmers have a background in shoeing and/or vetrinary background.They know what DOESN'T work and why, and really know anatomy.
Word of mouth will give you the best feel for the person in question. Just remember, nobody is perfect and there is likely to be SOMEONE out there that didn't like the trim or the person. But if the majority of the feedback is postitive, then procede.
Ask for references and actually check them. Find out how long the trimmer has worked on these other horses, how the owner found this individual, what they like and don't. How is the trimmer in handling the horses? Is he/she patient and gentle, but firm? Or too rough and rowdy?More than just a trim, you need someone you agree with in dealing with your horse. If you find the trimmer/farrier by referral, then they are worth checking out. People don't recommend farriers/trimmers they have lukewarm feelings about usually. I find I get LOADS more requests for business from word of mouth than any ad I ever put up.
Ask for the trim(and shoe if it's a farrier) price, of course, per horse. Find out if there is a farm fee (gas charge, trip charge, same thing, different name) and if that's affordable for you. Some will give a multi horse discount or waive the gas charge if there are enough horses to make it worth their trip. Don't be afraid to ask for a consultation. Look at is as a paid interview. Trust me. You'll be happier if you pay a gas charge to talk to this person, have them handle your horse and tell you how they would trim the horse before they ever cut anything. You can get that "gut feeling" and decide if you really want to hire them. If nothing else, you may have made a backup contact for emergencies (like when your trimmer gets pregnant *ahem*
Finding a trimmer on a list is a good place to start. No, I personally don't know anybody in your area. Sorry.Ask around at shows or events if you see a barefoot horse, ask the owner who does the work. Follow the basics of checking references and background and you are set to give them a whirl.
A side note for trimmers, ask them if they are familiar with fitting boots for their clients or not. That should be part of their experience-ability to get you in boots you will be happy with,if needed or tell you it's NOT needed. It can be a frustrating process. Just be wary of someone that only sells a certain brand for everything. I personally try to use the different styles and brands and don't have contract with a company, so I'm free to recommend whatever I think is best per horse/situation.