The song, originally known as "Gilligan's Island (Stairway)," created a minor sensation when it first appeared in 1977, and was primed to become a big novelty hit until Zep's legal team intervened.
After years of unsuccessfully trying to track down the 45, Polygram did me a huge favor when they somehow got permission to include "Stairway to Gilligan's Island" on a CD titled
Laguna Tunes, a collection of tracks that Kenny Laguna produced, wrote or played on. (Laguna is best known as Joan Jett's manager/producer.) The CD went OOP almost immediately, but can still be found for a reasonable price on Amazon and eBay.
http://www.amazon.com/dp/B0000457GF/?tag=imwan-20