Well, to me its a bit like going to Staples and asking specifically for "paper for my Laserjet 1300". AFAIK, there is no such thing as "paper (specifically for) (your) Laserjet 1300". There are different grades of laser printer/photocopier paper and they work in just about every laser printer in the world.
Of course, in the case of the 1571 you should not use high density disks and its preferable to use double-sided disks. However there is no such thing (AFAIK) as floppy disks "for Commodore 1571" and DSDD 5.25" floppies will work well in just about every properly working 5.25" disk drives made prior to the advent of high density drives.
Unless, of course, I missed something extremely important and that wouldn't exactly be the first time.
Sidenote: I think this thread should be in the "wanted hardware" section.