Steam Deck natively recognizes the PS3 controller. Simply plug it in via USB, wait for Steam OS to recognize it, then unplug USB cable and it will work over Bluetooth without needing
Gamestop G3 Gamecube Left and Right Trigger Replacement - iFixit Repair Guide
L1 R1 L2 R2 Bumper Trigger Buttons and Springs Repair for Sony PS3 Parts | eBay
L1 L2 R1 R2 Bumper Trigger Buttons + 2 Replacement Springs for Sony PlayStation 3 PS3 Controller: Amazon.de: PC & Video Games
1 SET L1 R1 L2 R2 Bumper Buttons Replacement For PS3 Controller Trigger Buttons | eBay
L1 R1 L2 R2 Bumper Trigger Buttons and Springs Repair for Sony PS3 Parts | eBay