Hmmm, I can think of a couple of ideas but they would probably involve some sculpting, as a heads up!
The Perry plastic WotR men-at-arms would have the period-accurate armour (and there's a mace-hand, and one of the bodies has a livery coat, like in the Osprey cover), so you could potentially use that, and add a head-swap. The Statuesque Miniatures Pulp-Scale Female Heads fit pretty nicely on the Perry bodies, so those could work for a headswap (though you'd need to add the crown yourself).
Alternatively, you could potentially get away with using a Joan of Arc figure and adding a crown, the armour would be a few decades out-of-date though
I'm not sure if there's a way to get the big flowing robe/skirt from the illustration without sculpting, if you're ok with that! Unless you did something like chop the Perry Margaret of Anjou figure in half and add the armoured torso to the top (she's riding side-saddle though, as a heads up there!)