build vnc4server from source

I want to build vnc4server from source, but am surprized that I'm unable to find the source code. Background: - I'm running TinyCore linux for a few years on a 32bit embedded devices. It's running vnc4server for remote access. - The 32bit embedded devices are not available anymore, so for new projects we're looking at a switch to 64bit devices. I'm setting up TinyCore in as much the same setup as the old devices. But now vnc4server is not available as an app for TinyCore 64bit. I've had other such apps (atftpd, bftpd, ...) which I just built from source. However I can't find the source for vnc4server. It seems to be part of ubuntu. It seems to be based on realVnc, of which I can't find the source as well. Any ideas where to look? Or any ideas for the closest alternative vnc server?