I have a '64 Olds too, and it has all of its original lenses for the dome light, as well as the map and the optional courtesy floor (under-dash) lights package.
You can obtain replacement lenses from:
USA Parts Supply
261 Industrial Boulevard
Kearneysville, WV 25430
www.usapartssupply.com
800-872-2013
I have been dealing with these guys for years, and actually recently purchased a dome light from them which is an exact duplicate of the original.
Hope this helps!