I offer it all the time..they are with different breeds that love it. I hope eventually they will..With this weather I worry about nutrients. They are not outside that often and very little to find out there. The older birds do not have trouble finding things..just those young things..and especially these HRIR for some reason.I wouldn't give up on them! Sometimes when mine have refused something ...avoiding it like the plague and giving it the "evil chicken eye"... A couple weeks later they eat it like it's going out of style.
Now...I know you probably have offered it over and over but...some folks give up the first time and never try again and those chickens are...well.... chicken when it comes to new stuff!