If you can deal with Mailorder:
http://www.affordablesurplus.com/syncom_floppy_diskette.asp
And, Athana still seems to be selling them as well:
http://www.athana.com/html/diskette.html
Regards,
Al
Phila, PA
  From: Warren Wolfe <wizard at voyager.net>
     Anyway, diskettes are going the way of the dodo.  I have several
 older machines, and spent a good part of the last two days trying,
 unsuccessfully, to find 5-1/4 inch diskettes for sale.  They simply are
 not carried any more.  And, I live in the heart of a truly major retail
 center -- I've been in EVERY major computer and electronics store, and
 many of the minor ones in the last 48 hours.