Hello DrHenk

Maybe a member has better info than I have.
Finding NOS link belts is unlikely now.

When I first looked at the Rover HD 25 the most obvious oddity was the
link belt. I had never seen one before on a rotary mower, but it made
sense for the application. It was old technology by the 1960s.

[Linked Image]

Acquiring a link belt for this mower should not be a great problem.
https://www.powergrip.com.au/PG_Transmission_BTR.htm

A local power-train supplier (like a bearing seller) should
be able to identify the pulley profile for a top-ling belt.

Hope this helps.
--------------------------------
Jack