I heard oranges are good for people at risk for strokes. Are they good for tias too?

I suppose so. Strokes and tias are, at their underlying cause, basically the same thing. Both involve clots impairing blood flow to brain cells. Tias are just when the clot fortunately dissolves in enough time such that no permanent damage has occurred. Oranges are in general probably good and better than foods with high salt, fat, sugar or cholesterol content.