per the APA book of standards the minimum weight for a BJG Rooster (over a year) is 13 lbs. a little less for a hen.
Look up BJG breeders-t I think there is a club.
Think about attending the Ohio National Poultry Show - the largest in the country - held in Columbus, in Nov every year - it is a 3 day affair I think. We attended as visitors a few years ago, and it was a great learning experience.
Look up on the NPIP website. There is a way to search by state. You will look up the stock codes on the left side ..I think the codes you are looking for begin with “R” they go by breed, then color. Once you have the codes(s), you will go the the states you are interested in, and search the document (using the bar menu at top of page, use the “find” function, type in the stock code and it will find all instances of that code in the doc). This should yield some results for you with addresses, and sometime phone numbers.
I’ve had some beautiful and very big BJG. Yes, to get the right size and shape, you will need a breeder, not a Hatchery. FWIW a BJG takes about 18 months to fully grow. If you want to show them, this matters.
I recommend buying the APA book of standards if you are wanting birds that conform to standard, this will be your guide.