Try and install Plasma from a live CD provided by several Linux distributions.

Plasma 5.7

In General

Fedora

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

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.

http://neon.kde.org/download

Kubuntu

Kubuntu 16.04 supports Plasma 5.6.5 through Backports.

openSUSE

openSUSE Tumbleweed ships the latest stable Plasma 5 release.
openSUSE Leap ships Plasma 5 but without live images.
Argon and Krypton are openSUSE live images shipping the latest KDE software from git (unreleased) for Leap and Tumbleweed, respectively.
While Argon and Krypton ship unreleased software build from git, Krypton stable provides builds of the latest released version (Alpha, Beta)
SUSE Studio Gallery contains various appliances with KDE Plasma desktop.

Slackware

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).

KaOS

KaOS is a rolling, independent, built from scratch distribution, focused on Qt and KDE. It makes regular ISO releases available, so any (new) user is not confronted with a large or complicated first update.