Moosa,
You can not purchase parent stock. You can only buy the end product of the line breeding for the laying offspring. The offspring are a product of hybridization of two or more lines of birds. It is my understanding that there is a male line and a female line in layer type chickens. The companies cross chicken A with Chicken B ( male line) to produce male chicken C. They cross chicken D with chicken E (female line) to produce female chicken F. They then cross chicken C with chicken F to produce the chickens you would buy to lay eggs.
I would suggest that you follow the advise of a previous post. Start small and learn, then grow your business.
I was in the health food egg business for a few years.
If you are going to free range, you will have to rotate the birds from area to area. If birds stay on one area, they will destroy the grass, etc. and you will have bare ground and nothing for the birds to eat.
I would suggest you start with 25 birds. Learn and then build the flock. I would run at least one rooster with the birds. Roosters will warn the hens concerning predators.
Predation will be a problem with free range birds. Your birds will need a secure area to roost at night ( a well built building).
Parasites will be a problem. Both internal (nematodes) and external ( lice, mites)
Sick birds will also be another problem ( respiratory infections).
You will have to become your own veterinarian.
You have a lot to learn. The least of your worries is the 300 eggs per year.
In Europe ISA is big- buy some ISA browns (they are a hybrid) which are excellent brown egg layers. Work with them and see what happens. You will have to rotate your birds every 1.5 years. ISA browns are the cross of a red male parent stock and a white female parent stock.
You could experiment. Cross an ISA brown male with some ISA brown females. Raise up the pullets- cull all the males. Then see how they lay.
If they lay well enough, then just purchase ISA brown for breeders. You will then rotate the offspring from the ISA brown crosses. The offspring will be various colors- some red some white some red and white.
You are going to have to find a buyer for all of your birds that you rotate out and males from the laying stock. If you have 300 layers that means you will have to find a buyer for the birds or process and sell the birds as stewing hens etc.
You have a lot to think about.
Try this site:
http://www.bovans.com/
Tim