Stephen, KiwiStar Optics aluminises mirrors. They did my 24 inch mirror. From memory they charge about $20 per inch of mirror diameter.
Here are the details:
Dave Cochrane
Optics Fabrication Manager
KiwiStar Optics
60 Gracefield Road
PO Box 31-310
Lower Hutt
New Zealand
Phone: +64-4 931 3735 begin_of_the_skype_highlighting +64-4 931 3735 end_of_the_skype_highlighting
Email: d.cochrane@irl.cri.nz