Is there a way to purchase additional walkers only? I've crafted my own walls, which were featured on CMON's page a few weeks ago:

However, Black Plague hallways are already crowded with walkers even without the walls. As much as I enjoy my walls, they only compound the problem. It's primarily the walkers that are the concern. If I could acquire another 20 walkers or so, I'd like to cut their bases off and place ten of them on a single base all bunched together to be a walker horde. Does anyone know if CMON has a method to buy specific walkers like that?