I dont want to build from source and was looking to find some repository where I can simply do an
apt-get install php5 and get the latest version. Does anyone know of any reliable source I can use to do the same or is the only option I have to build it myself?
There is PPA (Personal Package Archive) repository with PHP 5.3.6 at https://launchpad.net/~bjori/+archive/php5 with installation instructions. As I checked there is amd64 build as well (lucid).
Note that you need to enable universe repository for that.