I have a current flock of Partridge Rocks and Australorps and three turkeys.
I did lose some at first to hawks but built a netted area for them to escape to, discouraged the hawks with hung DVDs and I haven't lost one since.
You don't say how many you had, how old they were, how long you'd had them before you turned them loose, and what cover you gave them to go hide under.
Evading Hawks is a learned skill. Some LOSE that battle before the others learn. Now mine are all very careful to get under cover if one screams hawk. I have nine acres and lots of predators but mine are doing pretty well on that score.
Buff is a really visible color from the sky...
I have a free range rabbit, she's white, I figure she'll get it first before my birds do.
Learned skills require learning.
You can set up the environment to help them survive til they learn with brush, bushes, lean-to's or pallet structures to hide beneath. Netting or twine over an area keeps hawks from dropping on them. Reflective things discourage hawks, their sight doesn't like that.
Try again. Any of the major heritage breeds should work out given care and time. RIR OEGB, Rocks, Wyandottes, NHR, cochins do well free ranging, the Brahmas, the Giants, if you want eggs and not typical dual purpose birds then the giants tend to discourage predation due to sheer size. Or a nice big toulouse (sp) goose. NOBODY messes with them. They make excellent guards but they will bite the mailman.
I want a toulouse after I put in the wading pool for the dogs...
It can be done. They do learn. Stupid birds DIE but that's nature.