I suspect that RIBA does not produce anymore beach catamaran masts.
Since the last two years BIMARE catamarans are fitted with BIMAST (in house built) sections.
The new masts are better than the previous RIBA (6 bar pressure, more expensive carbon pre-pegs etc.)
I remember that a press release with full details was delivered a few months ago. If you can't find it, ask Matt McDonald of Vectorworks, which is NA BIMAST agent.
Anyway the BIMAST Javelin 2 stick in Europe has a retail price of EUR 3,300