Tara, if you decide not to go with the tubular tires you may be able to find a suitable set of 700C clinchers at a local bike co-op, or you could check out the website of the guy who posted just above this, Randy Jawa may be able to help you out with a set of wheels.
One other thing, your Gitane will probably have either a Huret or Simplex front derailleur, if its Simplex and has a black or weathered greyish clamp holding it to the seat tube, take a very close look at the clamp, they often cracked where the clamp bolt screwed in.