This is really difficult because most people don't want to be seen as an "experiment" for a straight couple. If you want to have a single experience with someone I would suggest a swingers party or advertising on a website but be aware that the girl may not be comfortable with all your requests! Good luck : )

Be upfront with the person in question about exactly what you're looking for.

It works best if you are already close friends with the person and there's no pressure on anyone. I'm not sure how to befriend someone new and bring them into that situation without them seeming like a throwaway/experiment.. I can never be sure if the "connection" is there with new people even if I am physically attracted to them.

You should definitely let the other person know up-front what your intentions are, and it would be best to find someone who is looking for something similar- another chick who would give this a try and learn something about herself as well rather than someone who may be more attached to you so be careful not to lead anyone on, they should know what they are getting into. Other than that, be safe and have fun

Start by making sure you and your significant other are on the same page (it's never fun getting a surprise in the middle of naked-time) so feelings don't get hurt. Talk a lot. I think a close friend that you think might go for it (and both of you like) is the easiest way to start. Put a bug in her ear, no pressure, and wait. That's how I ended up trying it out (it was rolling around in my head for a year first though).

I would go about by talking to a friend who is bi or lesbian and ask their opinion