Bits and pieces
While trying to find that website about JSC's Saturn V, I found this.
Only one Saturn V, at Johnson Space Center in Houston, Texas, has a complete set of flight-ready hardware. Its first and third stages (S-1C-14 and S-IVB-513) had been assigned to the cancelled Apollo 18 mission. Its second stage (S-II-15) came from the SA-515 Skylab backup booster.
Apollo 18's second stage (S-II-14) is displayed with the restored Saturn V at the Kennedy Space Center (KSC) Saturn V Visitors Center in Florida.
The (formerly) flight-ready backup Skylab itself is in the NASM in DC.