Welcome to BYC!!!
There are several options for purchasing coop ready birds - you can source them from some hatcheries, but the expense will be considerable as the price to purchase and ship birds at that age is much higher than that of day-old chicks. A better option for you, cost wise, would be to find someone near you who has birds they are wanting to sell. Where are you located? You can find other members here on BYC who are in the same area by posting to the "where are you/where am I" area - you may also find poultry groups for your area on Facebook and you can find birds for sale on Craigslist.