Yes, they are in the downloadable files, in pico-sonic-png.zip. It’s a multi-cartridge game so it’s actually a set of many cartridges (for code and data).
However, to run the game you need a patched version of PICO-8, because I went overboard and the ingame cartridge has more tokens than allowed. The patch would extend the number of tokens allowed (and also doing fast reload of data to avoid a short freeze each time you change level region). That’s cheating in a sense, but I’m still following the (compressed) characters / cartridge size restriction.
Unfortunately that prevents me from posting the game as a proper cartridge on the BBS, and you from playing the game from your player… Sorry for the inconvenience.
Note: there are more info on patching on https://github.com/hsandt/sonic-pico8#releases but it’s still incomplete (missing patches for Windows editor, etc.), and I don’t expect people to go to that length either. So the binaries are still the definitive version for this game.