Brake pressure bleeder adapter

Bit of a long shot but does anyone know where I can get a master cylinder adapter for a pressure bleeder for the S2000? The reservoir cap is a sort of bayonet fitting with a 56mm ID rather than a screw cap, I believe that is a Honda specific design that has been used since the 90s so is presumably the same as Civics, Integras etc of similar vintage.

I have found the CTA 7030 and Speedibleed C900 adapters however there are no UK suppliers and I would need to order from the US... arriving just too late. I've seen mixed reviews of the "universal" style Gunson and Sealey adapters too, horror stories of brake fluid spraying out over the engine and wings when it lets go so would rather avoid.

I've previously always done two-person brake bleeding but I've just found I'm going to have to do this one by myself, hence the late preparation.