Well in my opinion you are correct that it's not possible, as Tolkien not only never completed Quenya or Sindarin, he was very often changing his mind about things, and never intended that anyone should be able to speak it. What you might find is a lot of Neo-elvish, and you can read about that here...
http://www.elvish.org/FAQ.htmlThere is a bit of a debate as to what constitutes Elvish -- for one example (some points regarding Neo-elvish don't begin right away in the following link)...
http://movies.groups.yahoo.com/group/el ... ssage/1088For myself, I agree with Carl Hostetter on this point, as might be obvious by my comments and first link