Is this still available?
Most definitely! It is Polish or Dutch made and ships/sold in the US as a three box configuration with fuse plugs to connect them to fire as one single cake. 192 pounds in total:
Info is from the comments in this vid:
Apparently retails in the US for around $1000 but in the link that @n2ishun provided, it is 400 euros. Vendor seems to be in Poland. They probably need paperwork and licenses for importing though.
TXB869 BATERIA 600S 1.2″ TRIPLEX
Waga prochu [g] 8768 Dolot [m] 25 Czas [s] 300 Zapakowanie 1/1 Kaliber [cal] 1.2" Klasa ADR 1.3G Ilość strzałów 600 Kategoria CE F4
pyrozeus.com