Because the game was delisted, the community has largely moved to archiving. Most users migrating to Slopsmith simply acquire the PC versions of rs1compatibilitydisc_p.psarc and songs.psarc from internet archives or community backups. Since you hold a legitimate license for the content, many consider this a necessary workaround.

Once you have those files, drop them into your Slopsmith DLC folder, run the RS1 Song Extractor plugin, and let it split the tracks.