Building a vacuum assisted caster for silver and gold.

I'm having trouble finding a machined aluminum box for this vacuum chamber to fit around the flanged/perforated flask. I read somewhere about people converting pressure cookers into vacuum chambers, so I'm wondering if I can take an old pressure cooker and install a vacuum gauge and a line in for my vacuum pump.

I'll be hitting a few shops tomorrow to see what I can find that's large enough for this and still cost effective. I'm going to be using a 3" diameter flask with the flanged edge. Anyone know a good place to find one for cheap?