where are inmates under federal indictment held in the state of kansas?"

Depending on where you inmate was picked up, they will be taken to a federal detention facility. If your inmate is in Kansas, there is only one federal facility, it is at Leavenworth KS. But that really has nothing to do with what holding facility if the trial is not in Leavenworth. They will decide wher to detain them based on where the trial will be held.