With 700m head and 5cms flow (1000psi, 80,000gpm) and the water is fairly silty. The original was a trunion mounted ball valvetalking about an ANSI Class 600 equivalent valve (1440 psi rated pressure [1014m]).
FWIW, a Class 400 is rated for 960 psi [676m].  There is no Class 500, and actually Class 400 is rarely seen.  A lot of companies offer 150, 300, 600, 900, etc.
But back to the point . . . I wouldn't worry about getting an API 6D conforming valve.  There are plenty of water valves out there, and you don't want to pay for meeting oilfield requirements unnecessarily.  If you don't want to use a Chinese or Indian made valve (and I don't blame you), you might have a hard time finding a low-priced, general service water valve.
There is a company in Italy that makes large diameter ball valves, but it was bought by an Indian company (Virgo) several years ago, so they might have discontinued the Italian manufacturing.  There used to be a manufacturer in Brazil, but that was quite a few years ago.  ViNtrol in Oklahoma City sells the Virgo valves under their name, or you could contact Virgo Engineers in Houston directly, but they're amateurish to deal with.  Maybe a search for "Virgo Italy" will get you the name of the Italian operation.
I can't recall any other valve company names in the US, Canada, or England which might actually make the valves themselves.  A lot of them import parts from China or India and just do final assembly, at best.  On one that large, they probably import the complete unit.

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