Do you know that you can simply get the old mirror recoated with a modern, hard, protected and high reflectivity coat. If it has served you well and is a good 'figure' just get it recoated. I believe there is a guy in Taree, NSW (Wayne S) who has a recoating business, just ship the mirror to him and he will send it back recoated.
Have a look at this thread for details on recoating here in Australia and the contact details for them
http://www.iceinspace.com.au/forum/s...t=92288&page=2