TOURATECH do one, on page 302 of their 2020 catalog, a 1 piece seat...
Touratech SA may be able to assist you?
Be aware, it will likely be in a similar price bracket to that Rugged Roads (Italian) seat.
We can BUILD one, off of a 1-piece platform for you, but yo need a 1-piece BASE!
Cheers
Chris & Team
021 510 6455