Local trading papers often have livestock and pet sections so have a browse through there to see if there are any hens for sale. Also your local newspaper may have some private ads for chickens for sale.
Ask neighbours and friends if they know of anyone who keep chickens.
Go online to see if there are local breeders for you to go and visit.
Visit the Battery Hen Welfare Trust (BHWT) website to see if there are any rescue chickens that need a good home.