This demo is part of svgalib and can be found in the demos/ subdirectory of the original svgalib distribution. However, it is not installed in the system by default, s.t. it is unclear where you can find it if your svgalib was installed by some linux distribution. Even then, when you have the demo on your system, you probably won't have the sources s.t. it is only of limited use for you.
In case of any such problem, simply get an svgalib distribution from the net. You even don't need to install it. Just make in the demos/ subdirecty. As of this writing, svgalib-1.3.0.tar.gz is the latest version and can be retrieved by ftp from sunsite.unc.edu at /pub/Linux/libs/graphics and tsx-11.mit.edu at /pub/linux/sources/libs which will most probably be mirrored by a site close to you.
svgalib(7), vgagl(7), libvga.config(5), threed(6), accel(6), bg_test(6), eventtest(6), forktest(6), fun(6), keytest(6), scrolltest(6), speedtest(6), spin(6), testaccel(6), testgl(6), testlinear(6), vgatest(6), plane(6), wrapdemo(6), vgatest(6), mjoytest(6), joystick_init(3), joystick_close(3), joystick_update(3), joystick_sethandler(3), joystick_setdefaulthandler(3), joystick_getnumaxes(3), joystick_getnumbuttons(3), joystick_getaxis(3), joystick_getbutton(3), joystick_button1(3), joystick_getb1(3), joystick_x(3), joystick_getx(3).
The svgalib joystick handler was mostly done by Daniel Engstr\"om <firstname.lastname@example.org>. Multiple joystick, VC switching support and code to glue it into svgalib by Michael Weller <email@example.com>. Part of the code is based on code from C. Smith and Vojtech Pavlik.