If you do not find exactly the original CB for SL2, you may consider other older Mistral CBs.
The most precious one were the carbon (black) ones original to SL2, like on my picture, due to their outstanding performance.
The other ones (white) are from My Mistral SL1s (stock & Racing one), Mistral Competition TCS. Late 1980s
Major difference is the pivot ring on SL2 is wider in diameter but you could add a ring around one from 1980s.
Another difference: From 1980s CBs had those spring loaded pressure buttons (in different colors and different loads).
In the USA, in recent years, only WindpowerWindsurfing had some remanufactured parts for old Mistral Boards. Also a lot of Mistral old used boards and used parts. To my knowledge, they used to be Mistral Representative at least for the USA.
Unfortunately the website is down now:
www.windpowerwindsurfing.com
Good Luck!