Cup master cylinder port blank, where from?

[len_beach]

I'm about to fit a Cup master cylinder and Cup racer brake lines which require one of the rear ports to be blanked but where can I get one from?

i've searched eBay etc to no avail.

 

[BIGASH]

I used a bleed valve has worked perfectly and actually has some air in when I bled from that valve

 

[NorthloopCup]

I think they're m10x1 thread if that's of any use. Tweeks should sell them I'd have thought.