I was in ASDA supermarket this week and there were 2 packets of girls 8-12 L/XL underjams on the clearance counter. Half price (reduced from 5 to 2.50) but they were perfect sealed packets, not the usual bashed tins / torn boxes etc. Then I looked on the main shelves and there wasn't any. Maybe a new style is coming out or more likely they are discontinued as they already have Drynites and their own 'Bedtime Pants'
Looking on the mysupermarket site, it seems that Tesco supermarket is the only big place to buy them now.