Yeah, he comes over hunting for them quite regularly & has an English agent here looking for them too. Many a time I've been looking for a JB part only to be told that Greg got their before me, especially in the Birmingham area where Birch was based.
I've told him about a couple that I've spotted in shops which he's gone on to buy, this was the last one (a Gibson customised by John) a previous bass was lost in transit from Denmark to the USA.
But for the main part you're right, John Birch is a UK & to a lesser extent European thing.