Perhaps have a look at the Minairons website. Many of their aircraft are resin kits, but mostly in three large pieces and a few smaller bits. I think the Zero model I saw was in 9 pieces all in. Sorry, I can't think of one-piece castings as your question. I have seen them over the years, I think. Certainly one-piece AFVS and transport vehicles in metal, but I can't recall the manufacturer.