...but AFAIK it's out of stock in the EU.
Does anyone know a place where I can buy it (inside EU) ?
There are currently 42 observers in the marketplace so I'm not counting on getting a second hand one...

Marked available at London Modular https://www.londonmodular.co.uk/shop/three-sisters/

Thanks. I've also found it on Cymru Beats when I expanded to UK (it's always cheaper with €). The prices are a little higher in UK but it's still cheaper than importing from US.