There are no rebuild kits for the SE-i fuel shut off valve. I posted on your other thread what I did to resolve the same issue on my '85 LTD FI bike. The fuel shut off valve is significantly larger than those used on the carb models, or other years of bikes. I turned the 4 hole diaphragm over, reinstalled with a new sealing o-ring and all has been good for some 3 years now.
The fuel shut off valve is for doing work/maintenance on the fuel system - have to have some way to stem the flow of fuel when you work on the system. Other than this, leave it open and enjoy the ride.
Here is a good place for o-rings https://www.oringsandmore.com/metric-viton-fkm-orings/
If you get a cheap set of digital calipers it will be easy to measure the inside diameter of the valve knob & the thickness of the o-ring.
As for the 4 hole seal go to K&L. They have a few different sizes.