I may be able to build you a correct rear wheel. I'll have to see if I have the spokes. But you just need a square 28h rim and Shimano 333 rear freewheel hub. I have them both. I might have the rear spoke protector, which is, I believe, a 333 double-notch (shown below)
Derailleur would probably be a Shimano 333 or Lark. 333's are hard to find. There's a couple NOS Larks on Ebay right now, but I can probably put one together... just not as pretty.
Brakes would probably be an Excel set. (Gran Prix / Raceur) I don't think I have a complete set.
Seat... I haven't seen a green one like in the picture. Ebay is your best bet, but I keep an eye on those kinds of things.
Shifter... I don't even know who makes it, but it looks like this.
