Retail source code
https://github.com/philosophofee/SBSPSS - The source code repository for the PlayStation 1 game, SpongeBob SquarePants: SuperSponge
https://github.com/dizzy2003/MuckyFoot-UrbanChaos/tree/master/fallen/PSXENG - MuckyFoot's 1996 Urban Chaos PC, PSX and maybe DC sources
https://archive.org/details/warcraftIIsourcecodePSX - Blizzard's 1997 game Warcraft II PSX source code
https://archive.org/details/ReVoltXboxAndPCSourceCode - Acclaim's Re-Volt source code, PC/Xbox version but some PSX files remain in the archive
https://tcrf.net/360:_Three_Sixty - Cryo Interactive's 360: Three sixty sources as found on the retail CD
https://archive.org/download/Redump.orgSonyPlayStation-PAL-C/Chill%20%28Europe%29%20%28En%2CFr%2CDe%2CEs%2CIt%29.zip - Silicon Dreams studio's Chill sources are on the retail CD, in bags/cdfiller.dat
which is really a zip file.
https://github.com/RetailGameSourceCode/BattleKonchuuden - Battle Konchuuden's sources as found on the retail cd
https://github.com/RetailGameSourceCode/UltimateMortalKombat3 - Ultimate Mortal Kombat 3 's incomplete source code
http://www.psxdev.net/forum/viewtopic.php?f=41&t=470 - Beatmania APPEND 5thMIX - 1999.11.25 Psy-Q Source Code
https://archive.org/details/acclaim_discs - Acclaim's quagmire engine sources and assets
https://archive.org/details/Various-Mortal-Kombat-3-Source-Code-Collection - Various Mortal Kombat 3 Source Code Collections