Sealed units (Presteigne LD8)

I am looking for sealed units that are in good condition (not getting condensation) I can use to make a central panel in the ceiling of the pagoda of the garden at The Welsh Marches Japanese Garden: Where the Whale Talks to the Stars.

The pagoda was made in Japan, probably near Nara and exhibits amazing Japanese joinery. I want to make the building insulated but I dont want to hide this. But I also want to leave the roof ventilated so the sugi (Japanese cedar) remains good for hundreds of years (it’s 50 years old now and no sign of issues!). So my solution is to have a central panel of two sets of sealed units with 15mm in between. Even with older units, this will create high insulation. So I need two good sealed units no larger than 1200mm or smaller than 800mm in good condition. Maybe someone is changing out a window for an extension and and can help.
Can you help with this request?
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