In the whole Spyro the dragon trilogy for the PS1, there is basically one skybox that looks like this.
better than most other "skybox" "textures" found on this website.
of course with "retro" the author meant crazy colours and not something you'd actually find in games like Ace Combat 2 or the majority of Retro Systems skies, instead he meant some nu-retro shit that is useless for all except vaporwave shenanigans.
use gzdoom and load it as an iwad. ZDL may help you with that.
you can get it anywhere. Gog, Steam, Retail...
That would be nice, BUT we need for this game to get better before multiplayer.