I can't find a movie I downloaded and iTunes wants me to purchase it again.

I bought the movie, Stripes, a long time ago, and between backing it up to my external, then moving it back, and then deleting it from my laptop to free up space and moving it back again, I've lost it. I expected to find it back up on my external drive, but I can't find it. When I go to Check for Available Downloads in iTunes, of course it tells me that all of the purchases have been downloaded for this computer. I'm also concerned that I don't know when exactly I bought the movie, or if I still have a receipt in my inbox somewhere, so I'm worried that I won't be able to convince iTunes that I did buy the movie, and that they'll charge me for it again. I already own the movie, I just can't find it anywhere on my computer or external.