Your best bet would be to ask this question on the local board of your area.  Or plan a vacation and ask the question on that board.  I do my hobbying in Vegas, and know a bunch of ladies who would be willing to  play with you.

As far as asking about what you want that really depends on the lady.  I would be cautious the first time as they don't know you.  But if you build up a bit of a relationship then ask.

You can start by doing a search in your area here on TER, when you do the provider search form make sure you choose you city and two girl action. Read their reviews and visit their webpage I have found that most of the providers that are considered really bi are into working with a couple.  Some Providers will want to talk to both of you to make sure you both agree and some will ask what are your rules, she will most likely have rules of her own.I always try to contact them through email first ,after they responed then give them a call.She may ask you what you are looking for and want to get into the details. I would not try to plan a step by step encounter because it is best to let it flow naturaly.