If it was purchased on the iTunes Store, you may be able to use this feature:
If they weren't, sadly, they won't be available from iTunes as iTunes is only a program that interfaces you with your items - not necessarily stores them. Not unless you have iTunes Match, that is, or they were purchased from the store.
I do have iTunes match yes. But when I try to play some tracks it's still looking for the local file..
If I open iTunes on another machine and sign in they are all there, available and downloadable.
I guess I just delete all my info from iTunes on my own mac and let iTunes match repopulate it. Obviously I'll keep what tracks I have backed up along with libraries. That make sense?