Unless you got a lot (and I mean a LOT) of extra cash lying around, "hiring" an orchestra is out of the question. One way is to enter composition competitions (google some) and if you win, they'll probably play your piece and record it. OR if you know a music director/conductor with an orchestra, you can always ask them to perform your work (a little groveling/bribing/greasing doesn't hurt).
Before you do all of this though, I would strongly urge you to hone your orchestral/composition skills so you have a higher chance of getting your work played.