Bar End Brakes

I'm looking for some bar end brakes to go on bullhorn handlebars but I want them to screw around the bars rather than into the ends so I can also fit some bar end shifters. Do such things exist, I can't find any but my google-fu may be lacking for some reason.
Giant Defy Advanced 0 - Best
Planet X London Road - Wet
Montague Fit - Foldy thing that rarely gets used these days
Planet X London Road - Wet
Montague Fit - Foldy thing that rarely gets used these days
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*caveat: I've never used these type of bars before.
Felt Z6 2012
Red Arthur Caygill steel frame
Tall....
www.seewildlife.co.uk
Cannondale CAADX
Charge Plug 1
http://www.jtekengineering.com/products ... aerobrake/
There's also a version which mounts to some bar end shifters (though not the hub-gear-compatible one I used):
http://www.jtekengineering.com/products/aerobrake/
It was a pain to get hold of; I had to order from somewhere in the US and pay import duty. That was a while ago though, there may be a UK supplier now.
It was a bit finicky to fit; I had to file down the outside of my bars slightly.
Edit: SJS Cycles stock them in the UK. Not cheap though...