I believe that is correct. I have a very late production B7100 that had the ROPS kit installed which included the seat belt.
I have heard of folks finding new old stock on the kits but would guess that is going to be near impossible to find.
Yes, the END of production on B7100's has been basically 3 decades ago.
I would think finding a good ROPS off a salvaged B7100 is going to be your best bet at this point of time.
Kubota did have a safety program to supply ROPS for the B7100 but the web page on their site is no longer active.
It might be worth submitting a request on the National ROPS safety website to see if any of the kits are available.
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