To agree with what CMV said at the end there and some in the middle about a mixed flock. Last year I had a few of everyone, well mostly production heavy breeds. Mainly Australorp roos were dominate so now 1/2 my current birds (Which are all 1 y/o, nature happened that way) are Aust crosses, are laying like crazy. For us anyway. 5 weeks ago no eggs, bad weather here and terrible winter, then bang 2 1/2 dz a day since. Some of the birds are hatchery birds I purchased last year, some are farm hatched. I have a good ratio I guess because there seems to be no fighting with all my males, about 7, each has a group of 4-5 hens that stay with them and a few strays that wander where they choose.
I think I only have 1 pure rooster if I am lucky but for now they are keeping up with the feed bill, which isn't a lot because they get to roam completely free right now.
But like stated above, end goal should be realized if you want to hit a certain ideal flock. I had 1 last year, things happened and things changed now I am just content with my birds. So are my few customers and family, and that all that's important to me and mine. We are getting 60 meats tomorrow, for canning. Looking into 40 2nd year hens for more layers (On the real cheap side) and wife has agreed to 4 turkey poults next week from a local breeder. As well as filling incubators as I see fit, My mutts have always been kind and good to me, dogs and birds. I see no reason to change this after 35 years.
As for the grown rooster I have had that issue once or twice in the last few years, If your looking for pure breed flock, they can sometimes be a tough find, even if advertised . Last year we went to a seller that had RIR roosters listed, only to find out he had 1 he would never sell. Watch CL might get lucky. Or post an ad yourself.
Or 1 other option I forgot that comes yearly here, but in fall. A lot of 4f FFA kids sell their birds at the county fair after judging/ribbons. This could be a good option since these birds are judged and should not be as easy to get a crossed bird passed off as a pure. Just might need to prepare yourself for a higher priced bird if your looking for a breeder rather than just a flock rooster.