You can order a materials list and set of prints for any of their models for $15.00 plus $8.50 priority mail shipping. On the materials lists they call out the rough dimension and material needed for each part. The cast iron parts are called out as "castings" You can then order the materials from online vendors such as Speedy Metals, McMaster, Grainger, and others.
Their prints can be used with either components supplied in the kit or to fabricate components from raw stock.