I don't know where they keep vertical jump measurements ... If you want to find me any proof that he didn't have a 48 inch vertical, you really can't say otherwise. These aren't NBA archive sources, but here's what I found:
http://www.imdb.com/name/nm0150219/bio
"At his athletic peak, he was said to have been measured with a vertical jump of 48-50 inches."
http://en.wikiquote.org/wiki/Wilt_Chamberlain
* "What's unfortunate is that most people regard the great leapers as being only the short guys who could dunk," said the 7-1 1/16 Wilt Chamberlain. "My sergeant [vertical leap] was higher than Michael Jordan's. When I went to Kansas, they had a 12-foot basket in the gym, because Dr. Phog Allen was advocating the 12-foot basket. I used to dunk on that basket. It was an effort, but I could do it." [Source: The Leaping Legends of Basketball, The Los Angeles Times; Feb 12, 1989; Scott Ostler]
* Wilt Chamberlain claims that his sergeant, during his prime, was "46 to 48 inches, easy." [Source: The Leaping Legends of Basketball, The Los Angeles Times; Feb 12, 1989; Scott Ostler]
That's Wilt's quote. Take it how you want to take it. But, how about you give some proof that states otherwise.