We bought some hatching eggs from Poulet Anglais (based in Spilsby, Lincs) - we had to get eggs as we are in NE Scotland, but I think he does sell day olds too.
Hatching rate was good, and the chicks are very healthy & quick growing - think they got to a good weight by 10-12 weeks. His birds are a Hubbard type, and the one we kept had a good flavour, They free ranged over a section of the veg plot that was fallow & a bit grassy & weedy - the chickens loved it. The birds didn't go off their legs (Ross Cobb types may do this). But they did eat a huge amount of food - we fed them growers and mixed corn.
If that is the type of bird you're after, try contacting Simon Skinner at Poulet Anglais.
Sue