It's a shame that we don't have a contact in the aluminium casting business. There are foundrys on the web who will do low volume products, but I bet the tooling costs are eye watering.
My father, bless him, was a foundry man and a school mates father was the Pattern Maker there.
The Patterns (tooling) were made of a small smooth grain hardwood, so a good carpenter needed. - Not looking to damage the 'Mulfab' business, how about a Project for a Tech School or College near by you Dave?.
