Greetings Chris,
Here's some info:
http://web.archive.org/web/20050320215953/http://www.harpellassociates.com/a/a-fusible.htm
At the temps we use them, I don't think vapors are a problem. Search the web for fusible alloys and look at the MSDS sheets.
I've purchased it from MSC Industrial and eBay.
Later, Martin
'It used to be only death and taxes; now, of course, there's shipping and handling, too.'