One of the entries of Chris Strodder's Disneyland Encyclopedia that I checked closely was that for Lost & Found. I had worked there, of course, but several months back I discovered a Lost & Found location previously unknown to me. The book didn't mention this location, which wasn't terribly surprising. I don't know anything about it either!
The first photo is from February 1964 and clearly shows Lost & Found utilizing space in the Opera House.
I love that Disneyland logo! The display window is kind of interesting. At other times it displayed merchandise. Were the items in this photograph the lost goods of the day? Here's a close-up so you can get a better idea of the variety of things:
While the facade is part of the Bank of Main Street, that door is functionally part of the Opera House, as you can see from the following 2001 interior photo of the Walt Disney Story:
The display case sits on the other side of the wall here labeled "The Happiest Place on Earth." A year later, Lost & Found had moved (back?) elsewhere. This March 1965 photo shows all traces of the service removed:
...excepting, perhaps, some of the window display. Are those two dolls the same ones as in the 1964 photograph?
Lost & Found clearly had to go when Great Moments with Mr. Lincoln assumed tenancy from the Mickey Mouse Club Headquarters, but why was it there in the first place? And what in the world did the interior look like? That display case is still there, as is the door and the lighting fixture. Compare to this April 2007 shot, courtesy of Daveland: