It took me a while, but I found the right libsdc++ for the current free vnc 4.1.3, deep in this: http://mirrors.develooper.com/hpux/gcc-3.3.2-11.00.sd.bz
Merijn's HP-UX software Download Section for ITRC members is a rich source for old libraries.
So if you cannot find the right depot or tar or libgcc package, this is a great resource.