Hatchery

I think the suppliers listed on the Poultry Pages on the forum are mainly POL egg laying hen suppliers, but here is a link just in case :

https://www.chickens.allotment-garden.org/

Other than that, are there urban farms near you that may know someone?  The other option I can think of is a butchers shop where they sell locally produced chickens.  That might lead you to a supplier who can tell you where they get their birds from.  There are also people advertising poultry of all kinds on Preloved.

https://www.preloved.co.uk/classifieds/horses-livestock/poultry-game