Slackware Packages
Tux Paint for Slackware Linux is available as two packages, maintained in the unofficial SlackBuilds.org repository. One contains the main program (Tux Paint) and confiugration GUI (Tux Paint Config.). The other contains the optional 'stamps' collection.
You can download the latest version as source code and build it yourself. The latest verion is available as a Flatpak package.
Tux Paint
tuxpaint & tuxpaint-config
https://slackbuilds.org/repository/14.2/graphics/tuxpaint/
Version: tuxpaint 0.9.24 & tuxpaint 0.0.15 for Slackware (2020.06.15)
From: Tim Dickson
Rubber Stamps package
tuxpaint-stamps
https://slackbuilds.org/repository/14.2/graphics/tuxpaint-stamps/
Version: 2020.05.29 for Slackware (2020.06.15)
From: Tim Dickson
Did you know? Tux Paint is not shareware, it's open source. So it's free, forever!