Try and install Plasma from a live CD provided by several Linux distributions.
The Fedora KDE Spin comes with Plasma. New minor Plasma versions are pushed as regular updates for Fedora installations but live media may contain a slightly older release (depending on Fedora’s release cycle).
KDE neon builds Frameworks and Plasma on a continuous integration system for its Developer Edition.
You can use the stable version for builds from Plasma/5.x branches or unstable version for builds from master branches. The user edition has builds from released software.
Alien BOB (Eric Hameleers) provides an installable Live image for Plasma 5 based on the development tree "slackware64-current". Login account/password are both "live". Use su or sudo to become root (using the "live" password).