What do you call those expanding metal bracelets that printers (and
others) used to wear over thir shirtsleeves to keep their cuffs clear
of work surfaces? Where can I buy them?

Hi Bartie,
They are called "sleeve garters" (also sometimes known as "arm
garters"). Most of the searches on google turned up the fabric style
more associated with the Wild West (and most often used for costumes).

However, I did find a company that has what you need: John Helmer
Haberdasher Inc
http://www.johnhelmer.com/

They have a choice of silver, black, white or gold for $8.00/pair
(plus shipping):
http://216.239.51.100/search?q=cache:pvf6fCPv4A8C:www.johnhelmer.com/prod.itml/icOid/108+%22sleeve+garters%22&hl=en&ie=UTF-8

Hope this helps.

alex_p