Asda (£1) - empty.
Tesco (97p) - empty (except 2 of the first batch of 2012 on a strip).
Sainsbury - don't stock.
Morrisons (£1.09) - rather full tub, with some of a recent 2012 batch and some from a mid-2011 batch.
TRU (£1.25) - filled up rather well with current UK batch dated E17 on 16 pegs. Sadly this was already out at Asda before and purchased before so none needed.
Waitrose (£1.25) - about a dozen left from the first batch of 2012.
WHSmith (£1.99) - same 2009 models that have sat there for 3 years (wonder why at that price).
I used to go to Newmarket a lot for work, but found nothing in most stores. Halford's had a few peg warmers, WH Smith had a big bin of old stuff, and Moon's Toy Box had old stuff. Nothing in the Waitrose or Tesco.
Went to the TRU in Norwich and all they had was big sets, and a few singles. Ely had a nice toy shop, and Bury had a model shop with only kits and trains. Best I found was Langley's in Norwich. Might be a bit of a drive from North Wales...