Undrave
Legend
There are some spells and paladin auras you could repurpose as well.
The problem is, all of these things have already been rejected by warlord fans as insufficient (With the UA alternative class abilities and feats you can cobble those battlemaster manoeuvres onto a PDK). Colour me dubious you could make something from this that would satisfy even a small fraction of warlord fans. I would be fine with it though.
The problem is that they're all over the place and cobbling them together results in a wonky MC mess with subpar abilities. The other problem is that they don't really scale to match the challenges of the higher level. A Battlemaster that gains level just picks the maneuvers they didn't like LESS at lv 3 instead of getting new, better ones. And again, their's nothing you can do at-will. With a Feat and Fighting Style you get TWO superiority dice. That's it.
I would go for: At the start of each battle you may add your proficiency bonus to the initiative rolls of a number of allies you can see within 60' (including yourself) equal to your intelligence mod (minimum 1). You may do this before or after you see the rolls. I don't think that would break anything.
I could see the area of effect start smaller and increase with level.
I could also see abilities that trigger on rolling initiative. Like "When you roll for initiative, you and each allies within X (getting bigger as you level) that can see and hear you gains Temp HP equal to your CHA" or "Get to move half their speed without spending an action" or some such.