DS
Can't help you with the tar-mac, but on concrete, if the pavers/surface is white so no coloured pavers here you can use Oxalic acid or Citric acid. You cannot spot clean with eiter of these two acids as they will turn the surface quite white, you have to do the whole area because if you spot clean you would have loads of white dots etc.
Tensid do ferrous stain remover and a rust stain remover poultice not sure of the prices these days but they won't be cheap.
The other thing you have to work out is, is this a rust stain or a fertilizer stain (plant food, grass feed etc) as then can look very much alike. If it is fertilizer staining you might just have to live with it and let time reduce the staining.
If it is a rust stain then what is causing it? are they very old pavers with metal rods running through them, if they are the the staining could leeach out forever and a day. If the stain is where something metalic has been stainding then try either the acids or Tensid products.
You do find phosphoric acid in some metal cleaners like ally wheel cleaners etc, these might help reduce the staining also. OCH used to do a aluminium cleaner which I have used with some success.