unless there is no contact info.  Then and only then, you can ask the original provider for contact info.

Sometimes I look ad a provider's website or something and although I find her attractive (which is why i am looking in the first place). I feel myself drawn to a friend of hers or someone else listed on their site and only want to see that girl or at least see that girl first. Just happened to me as a matter of fact. I don't want to offend anyone, which is why I never asked. But I would love to her the ladies' responses as to how they would feel getting that type of request and the best way to do it. Thanks

Go for it!

Agreed! Oh and Please make sure you at least saw the girl once before asking about her friend. In a way can be kinda rude.

I know.  It can be a problem.  At the last mixer I raised this very question with someone I wanted to see but had to save up for.  She said about her friend "Go for it..I'm around all the time and she is just visiting".  I think the way to handle it is to clear it with the first girl.  Most providers don't mind knowing that it will come back to them either with you seeing them or their friend referring someone.  Being up front is the best way.