Recently my girlfriend informed me that she wants me to set up a three way, and to surprise her with who I pick. This is out of my field of expertise, and I would like to know how to approach someone for this. Also, neither of us are in any huge hurry to do it.
Well a blood test is definitly needed. STD's are real and deadly. She really wants sex with a stranger? Really? If you chose a person you know it might be safer but you risk emotional attachment. There are website dedicated to this sort of thing like AdultFriendFinder. There are probably a thousand people in your area available immediately. If it were me I would chose someone I know with the understanding it is a one time thing. My girlfriend and I were just discussing this our selves and decided her being a hot wife was better left a fantasy. The risk outweighed the reward.
Since there is no rush, take your time and plan this out carefully. You may discover the fantasy is better than the reality, especially as you weigh all the factors that Chuck presented. If she wants a MMF, it will definitely be easier to line someone up than it will for a MFF. If you don't want to involve a friend, and risk the emotional consequences, then go the internet route and 'interview' potential prospects carefully. But personally, I'd recommend expanding your social circle. Seek out new friends and get engaged in social activities with different people, feeling them out for such an adventure. Your girlfriend may want the spontaneity of a random fuck with a stranger, but the risks can be significant! Chemistry is everything in a threeway, and the odds of it just happening with a random partner are pretty slim. It can be a pretty awkward and embarrassing experience unless you choose carefully, or get very lucky!
Bethany and Chuck have given you great advise. Discuss this a lot more with your girlfriend. It is certainly possible to work this out and make it happen!