Wilson Combat Bullet Proof Ambi-Thumb Safety, Wilson stock # 192BBP. This part is new in original package. No better parts or guarantee than Wilson Combat. Be aware that some brands of ambi-safeties are prone to come loose after a little use - I have never heard that complaint from a WC safety.
Retails for $142.95 from Wilson and is currently out of stock on their site. Price includes shipping in lower US.
Per Wilson Combat: The Toughest Ambi-Safety You Will Ever Find-Anywhere!
Billet steel construction, precision CNC machined for a long-lasting, wobble-free fit. A unique hammer pin holds the right side lever securely in place without using the grips to hold your safety in place. Pre-shaped and contoured for a perfect, comfortable feel right out of the package. Some fitting may be required.