They have some in again at the moment ! The larger ones are between 3.5" - 4" and at £3.50 - so not cheap but they are lovely indeed
Maidenhead Aquatics in St Albans have them for £2.25 each.
Regarding the size, one of the problems with these new fish is that very few people have kept them. It takes time for them to grow and unless they are in a large tank with few other fish they may not grow as much as they might.
Also with fast moving fish you can quite easily overestimate the size. I would have said the wholesales fish were 2.5-3" Unless you take them out and measure them it is very hard to tell. (and feegradei dont take kindly to that!)
People can only state what they have experienced