Though they're a bit more "stone and iron gating walls" than just pure stone walls, if you ask me.
From the preview:
Stronghold Terrain: Stone Wall Preview
Here you can see a picture of our news Stone Wall products. They will be released on the 16.06.2012.
Stone Wall Set: 3 Resin wall sections + 4 Resin colums + 3 plastic fences (9,90 €). Together 28,5 cm long and 4 cm high
Expansion Set: 1 wall section + 1 colum + 1 fence (3,50 €). 9 cm long
Damaged Section: 1 wall section + 1 fence (3,50 €). 9 cm long
If you like it you can place a preorder at our shop.