I have always wanted to try a duo and I am looking for advice on the best way to approach finding two providers for a really great experience.  

and they all worked out well, but if I had to choose only one method, it would be for the providers (someone you already know pretty well) to pick out the third partner.

I don't think you need to try both providers , though i can not think of a more fun research project. If there is a provider you enjoy ask her. If she is truly bisexual that makes all the difference. I would love to offer my services to help you with this great adventure

You don't need to have separate sessions with 2 women to check out. In fact my only duo, I had good time with the girls individually, but they never clicked together. They weren't really into each other..  

Ask someone you have seen before to set up the second provider, exactly as Fisher says.      

who love doing duos together so much that they offer a duo rate that’s less than the sum of their individual solo rates.  And others who have different individual rates and that’s what they charge for a duo, plus possibly a travel charge if one has significant travel time.  

Having the lady I already know suggest a second lady.  
My sample is probably around 100 3somes--I've already had 5 just this year. When the lady I know brings a friend, the first lady already knows exactly what I expect to see.  

ladies who are friends who work well together. I would go with the second option.
The first option I have done before and it worked out well on most appts but there has been a few times where the lady is not really BI. She did not want me to touch her and the client is looking for a girl on girl show it was quite awkward.
When I do duos with a lady I have never played with  before I like to meet her before the appt to make sure we are on the same page. The times when it didn't work out the lady refused to meet ahead of time.
Lesson learned now I only with duos with ladies I am friendly with or have worked with before together.
Just my .02

Thank you to everyone has replied. I really appreciate your input! I feel like I have a much better sense of what will likely work. Obviously, everyone should enjoy the dynamic which will make the experience so much more fun.

I think I may have to take you up on that offer

Ask the PO at the org who on his team does doubles.  They usually have a pair that enjoy this.  I tried this once several years ago, and it was very mind blowing and stimulating.    Having one doing BBBJ and the other DFK and 4 hands roaming around was incredible.  I am a one pop guy, but I wanted to get in both.  They changed condoms between this.
Once I popped, I was exhausted.    I asked the girls to make out and do a 69.  It turns out one was bi and was really into it.  But what a show to watch.