Taking the advice of this post (mirror here, here and here), I went to Robert’s vintage Barbours on Portobello market in London. I went on a Friday in September of 2017, and, sure enough, Robert’s stall was right there under the Westway, off Portobello road, a couple of minutes walk from the Ladbroke Grove tube station. (Google map here.)
Prices ranged from £79 to £110 for all sorts of Barbour jackets – mainly olive, waxed ones (Bedale, Beaufort, Northumbria, Border – no Ashbys, as far as I could see) but some blue, too. Quality varies, but all of them are acceptable. Pay by cash – ATMs are to be found nearby.