We have a SL 1000 Vertical and I believe the Quick Italy remote control is the same as yours. In any case, the connector also has three pins.
Last year in June I stepped on it and suddenly it only had two pins. Fortunately we have a second remote control, so the problem wasn't critical. Since then, I've asked in many stores for a replacement plug. The answer was always, there is no more, everything has to be done again.
But that's not true. Coincidentally, the lady from the chandlery in Lefkas Marina had such a plug freshly ordered on the counter last Monday, which I immediately bought for € 10. Soldering is a bit fiddly, so I let a professional do it.
In short: the plug is still available.